Trace when the noise occurs and whether water escapes the air-gap opening before assuming the RO tank or membrane failed. Watts RO-PURE lists drain-tube restrictions and sink-drain problems for faucet air-gap noise. Preserve the designed air gap and reject flow. Persistent noise, leaks or drainage backup needs the actual model's installation checked.
Check whether this is a drainage problem
The Watts Premier RO-PURE troubleshooting table lists a crimp or restriction in the drain tube and a clogged drain associated with dishwasher or disposal use under noise/water from the faucet air gap. Those are possibilities for this model; noise alone does not prove one particular blockage.
If water comes out of the air-gap opening, stop the uncontrolled discharge safely and arrange correction. The existing RO air-gap guide explains the protective separation and named-model drain arrangement. This page focuses on recording the operating pattern before attributing a sound to a component.
Compare the exposed route with the manual
Look at tubing without pulling it loose. Note a new kink, displaced tube or low spot after work in the cabinet. Check the actual drain-connection location against your model's diagram.
The Pentek RO-3000/RO-3500 manual warns about drain connection locations that can receive backpressure from dishwasher or disposal operation. That is a routing question distinct from the membrane's output or the tank air charge.
If the assembly was moved to a utility room, compare the model-approved remote RO drain arrangement rather than simply copying the under-sink tube route. Relocation does not resolve a blocked receiving drain or remove the required separation.
Do not insert wires into assembled tubing, disconnect a pressurized path or pour drain chemicals through the RO faucet. A service provider should establish safe isolation and correct access before addressing the restriction.
Do not silence it by altering the designed flow
Never plug the air-gap opening or clamp the reject tube closed. The drainage path and separation are part of the specified system arrangement. Bypassing them trades the sound for a different installation fault.
If water keeps going to the drain after an apparent refill, use persistent reject-flow troubleshooting. If drinking-water production has also changed, report an unfilled tank or poor full-tank delivery separately.
Give the technician a useful history
Keep a safe recording of the sound, time since last water draw, escaped-water observations and any recent sink or cartridge work. Note whether the kitchen sink itself drains slowly or backs up. A corrected tube route does not establish that a separate building-drain problem is resolved.
After correction, the actual drain route, air gap, leaks and system operation should be checked together. Do not treat a quiet faucet as proof of every contaminant-reduction claim or normal tank function.
For an APEC ROTL-600 or ROTL-600PH, also distinguish its documented automatic-flush events and protection messages. The duration and indicator pattern must match that model; a sound alone does not establish normal operation.