Most under sink filter noises have a simple explanation, and you can often quiet the system in a few minutes. The most common causes are trapped air after a cartridge change, a partly closed valve or kinked tube, a loose fitting, or a drain line that traps water. Start by shutting off the water supply, releasing pressure, and unplugging any booster pump before you inspect anything. Stop and call a plumber or the manufacturer if you see leaks near electrical parts, a hot pump, a burning smell, or repeated cycling with low production.
A steady, familiar hum or a light gurgle is usually part of normal operation rather than a fault. A new, louder, or continuous sound marks the point where diagnosis is worthwhile. The steps below walk through each common noise, the first check to make, and the point at which you should stop and get professional help.
Turn Off the Water Before You Inspect Anything
Before you touch a housing, tube, or fitting, shut off the water supply to the filter. Then open the faucet to release pressure from the lines. Do not open a filter housing until the pressure is fully released and, where the system has pressure gauges, both gauges read zero.
If the system has an electric booster pump, unplug it before you handle tubing. Water and electricity should not share the same workspace, and a pump that keeps running while you work increases the risk of shock or a sudden leak.
Keep these stop conditions in mind throughout the inspection:
- Water leaking near an outlet, power cord, or pump
- A pump that is hot to the touch
- A burning smell
- The system cycling on and off repeatedly while producing little or no filtered water
If any of these appear, leave the system off and call a plumber or the manufacturer before using it again. Noise alone is not proof of danger, but these specific signs call for stopping the system.
Once you have a general sense of the system and the sound, match your symptom to the sections below. For background on why drinking water quality matters and how filters fit into the picture, the EPA’s drinking water information is a useful reference, though service steps should always come from your own manual.
Match the Sound to a Likely Cause
Use this table to narrow down the cause before you start taking things apart. Each row lists the first check to make and the point at which you should stop.
| Sound | Likely cause | First check | Stop when |
|---|---|---|---|
| Humming or buzzing | Booster pump running, clogged pre-filters, or low inlet pressure | Pre-filter condition and incoming pressure | Pump is hot, smells, or runs without stopping |
| Gurgling | Normal reject water draining, or a drain line that traps water | Drain line routing and the auto shut-off valve | Gurgling continues when the faucet is closed and the tank should be full |
| Whining or high-pitched | Tank pressurizing on a new install, or missing filters or membrane | Filter and membrane seating | Whine does not stop after a few minutes on a new system |
| Clicking | Auto shut-off valve or pressure switch cycling | System pressure and valve connections | Repeated clicking with little filtered water |
| Dripping | Loose fitting, worn O-ring, or faucet leak | Every connection and the housing lid | Leak is near electrical parts |
| Knocking or thumping | Loose tubing or water hammer | Tube routing and mounting hardware | Knock continues after tubes are secured |
| Rattling | Loose bracket, tube, or housing | Mounting hardware and housing alignment | Parts are cracked or a housing will not seal |
The sections that follow take each symptom in turn.
Is the Noise Normal?
Some sounds are expected. Reverse osmosis systems make slight noises as they process water, even when the faucet is off. A slight humming noise while water is dispensed is normal and comes from the pressure change inside the system as it begins processing more water. A slight dripping or gurgling noise at the sink drain is also normal, because it is reject water flowing down the drain.
Gurgling is the most common reverse osmosis noise, and it is almost always normal. It happens when waste water flows through the flow restrictor into the drain line. A low, steady hum usually means the booster pump is running as intended, since booster pumps increase pressure to push water through the RO membrane.
On a newly installed system, a whining sound can occur while the tank pressurizes for the first time, and it should stop within a few minutes. If a new installation produces a loud noise, the install may need adjustment, and a slight change to the drain line adapter can reduce the noise.
The rule of thumb is simple. A steady sound you have heard since installation is probably normal. A new, louder, continuous, or intermittent sound that started suddenly deserves a check.
Fix Humming or Buzzing
A hum that is louder than usual, higher-pitched, or running without stopping often points to clogged pre-filters. When sediment and carbon pre-filters clog, they restrict water flow to the pump, forcing it to strain against reduced pressure. Check the pre-filter condition first, and replace them if they are due.
Incoming pressure matters too. One under sink RO model, the AquaTru Under Sink, is designed to operate at roughly 2.76 to 5.86 bar, which means it needs a minimum incoming pressure of about 40 psi for the reverse osmosis membrane to function properly. Below 40 psi, filtration slows and output can drop to a trickle or stop. A plumber can measure incoming pressure to confirm the reading. These figures apply to that model specifically, so check your own manual for your system’s range.
If the hum continues after you have checked the filters, confirm that the shutoff valve is fully open and that the tube feeding the system is not kinked. A partly closed valve or a kinked tube restricts flow the same way a clogged filter does.
Fix Gurgling After a Filter Change
Gurgling right after a cartridge change is usually trapped air working its way out. Flush the new cartridge according to the manual, then run the faucet for the recommended period and let the system settle. The sound should fade as the air clears.
Persistent gurgling is different. If gurgling continues when the faucet is closed and the tank should be full, the auto shut-off valve may not be engaging properly. A drain tube with a sag or low spot can also trap water and siphon it back, producing gurgling long after the system stops producing water. Route the drain line so it runs continuously downhill to the drain with no low spots, and check the auto shut-off valve connections.
If adjusting the drain line does not settle the noise, and the system keeps producing reject water when it should be idle, contact the manufacturer. That pattern can point to a valve that needs service.
Stop Whining and High-Pitched Sounds
A loud whining noise can be caused by missing filters or a missing membrane. Check that every filter and the membrane are present and properly seated. If the system was recently serviced, confirm that no cartridge was left out and that each one is pushed fully into its housing.
On a new system, a whine while the tank pressurizes for the first time should stop within a few minutes. If it does not, and the filters are all present, the installation may need adjustment. A loud noise on a new reverse osmosis installation probably means it was installed incorrectly, and a slight adjustment to the drain line adapter can often reduce it.
If the whine continues after you have confirmed all components are present and the drain line is adjusted, contact the manufacturer rather than continuing to run the system.
Stop Clicking on a Reverse Osmosis System
Clicking is usually the auto shut-off valve or pressure switch cycling as the system fills and stops. Short, occasional clicks as the tank fills are normal. Repeated clicking with little filtered water is not.
Do not remove the flow restrictor to try to make the system run faster. That part controls the balance between filtered water and drain water, and removing it can waste water and affect how the system operates.
If clicking continues and the faucet produces little water, stop using the system until you have checked the manual or contacted the manufacturer. Checking tank precharge pressure and the shut-off valve is a job you should do only with your model’s manual open, since the correct pressure differs by model and by whether the tank is empty.
Find and Stop Dripping
A drip is a straightforward leak to trace. Work from the housing back to the supply line and check every connection: the housing lid, the inlet and outlet fittings, the tubing connectors, and the faucet itself.
If you have just changed a filter, double-check the O-rings and housing alignment before assuming a part is broken. Wet the O-rings with water or the fluid being filtered before seating the cartridge. Use only the lubricant named in your manual, since petroleum-based products can damage some seals.
Some manufacturers recommend changing O-rings each year, so check your manual’s maintenance schedule. If a housing will not seal after reseating, replace the O-ring rather than tightening further, which can crack the housing.
For a full walkthrough of leak sources and fixes, see our guide to an under sink water filter leaking.
Handle Knocking, Thumping, and Rattling
Knocking and thumping often come from loose tubing vibrating against a cabinet wall or another pipe. Secure the tubes with clips or padded ties, and make sure the housing is mounted firmly. Rattling usually traces to the same cause: a loose bracket, a tube touching something, or a housing that is not seated squarely.
Check the pressure rating on your housing before you assume the system is fine at its current pressure. A housing’s pressure rating is the manufacturer’s tested limit for that specific model, and exceeding it risks a cracked sump, a blown O-ring, or a sudden leak. A maximum rating is not a normal continuous operating target, because manufacturers build in a safety margin. The only reliable way to know your housing’s limit is to check the specification sheet for that exact model.
Reseat O-Rings and Housings Safely
If a noise started after maintenance, reseat the components before replacing parts. Shut off the water, release pressure, and confirm the pressure is at zero. Open the housing, wet the O-rings with water or the fluid being filtered, and seat the cartridge fully. Line up the housing threads squarely before tightening.
Do not use petroleum-based lubricants on seals. Use only what the manual names, and replace O-rings that are cracked, flattened, or stretched.
Check Pressure Against Your Model’s Spec
Pressure is behind several noise patterns, so it is worth checking against your manual rather than guessing. Colder water is more viscous and harder to push through an RO membrane, so output can be naturally slower in winter even when pressure is within the normal range.
If your system uses a storage tank, check that the tank is standing upright as designed. Laying it on its side can damage the bladder and stop the tank working correctly. Tank precharge pressure also differs by model, so use the manufacturer’s figure and procedure rather than adding air by guesswork.
If the incoming pressure is out of range, do not install a regulator or alter the main water line without the right parts and plumbing knowledge.
Reset the System After Replacing a Cartridge
After a cartridge change, follow the manual’s flushing time, then open the faucet and let the system run. Check every connection for drips while it runs. The housing should be hand-tight per the manual, not overtightened.
If a new cartridge does not fix the sound, confirm you installed the exact replacement part. Cartridge and part numbers vary by model, so verify the number against the manufacturer’s documentation before ordering another one.
When to Replace the Filter, Call a Plumber, or Contact the Manufacturer
Replace the cartridge when it is due per your manual or when output has slowed noticeably and the pre-filters are clogged. Noise that returns after a correct replacement usually points to something other than the cartridge.
Call a plumber if a shutoff valve is corroded or will not close fully, if the leak is near electrical parts, or if the repair requires cutting into the supply line. Replacing a saddle valve can require cutting and adapting the water line.
Contact the manufacturer if the system clicks repeatedly with little production, if the pump is hot or smells, or if the whine or hum continues after filters, tubing, and pressure have been checked. Those patterns point to a valve or pump that needs service.
For a broader comparison of system types, our guide to reverse osmosis vs under sink water filters explains how the two differ in parts and noise sources. Checking the filter’s inlet tubing and fittings for kinks before calling anyone can save a service visit.
The Quickest Path to a Quiet Filter
Shut off the water, release pressure, and unplug any pump. Then match the sound to a cause: hum to filters and pressure, gurgle to draining and the auto shut-off valve, whine to missing parts, click to the shut-off valve, drip to fittings and O-rings, and knock or rattle to loose tubes and hardware. Reset and flush after a cartridge change, and always get tank pressure and part numbers from your own manual.
If the noise is new, loud, or paired with a leak, heat, or a burning smell, stop and get professional help. If it is the same steady sound the system has always made, it is probably normal operation.
