We had that. Only in kitchen. It was old deterioring rubber in compression hose. Another test is do this: take a glass of water from that faucet etc. let it stand overnight. Don’t drink it but the next morning take a sip (then spit it out). If it tastes plastic or rubber, it’s hoses. By the way, hot water leads to heater but also rubber washers and hose lining deteriorate faster on the hot water side! And he could not see that in inspection unless he disconnect the hoses and looks and the rubber and the line. If hoses, Home Depot has decent ones but you must get the correct connectors on the end. Shut off you water supply before disconnecting …to state the obvious. Watch Brasscraft video for tighten procedure. Remember that. Happy hunting.