There is no way for air to get into the system, unless you pump it in, so there is nothing to get out. The washer on that faucet is either loose or worn to the point that the edge is vibrating like the reed on a musical instrument. Turn off the water valve under the sink and replace the washer. Unless it is a Price-Pfister with the washerless stem. In that case the coating on the stem has deteriorated and you need a new stem.: I tried to shut off the main line and turned on all the faucets to let the air out,but it didnt quite take care of the problem. Please help. It only happens at one faucet, not all the faucets in the house.