f73a157e_ion_and_Trouble_Shooting_Guide__PROBLEM
[CAUSE] - Air gap faucet. - Drain tube. [SOLUTION] - A little noise is common with air gap faucets. Check manual to be sure installed in proper location. Allow two weeks for air to work out of system. Check that drain tube from faucet is continuously down hill to drain saddle. Loops or dips will cause noise and back up in drain line to faucet. [PROBLEM] 
Noisy drain or faucet.
Water Filter and Reverse Osmosis Installation and Trouble Shooting Guide
PROBLEM