Need help! I hear humming noises when I turn on any 2 or more faucets (toilet flush with turning on faucet or a kitchen faucet along with an upstairs faucet). Only one faucet or one toilet flush no humming noise will occur (only happens when on together). I've shut off the main drained all water in house re-opened (completely) the main and still humming noise when I open 2 faucets or more. One thing that does differ from having two outlet running at once is when I turn on the hose bib in the front of the house. This humms regardless if nothing is on. I turned off all three bathrooms and opened 2 faucets and still humming noise occurs. I checked the pressure and adjusted it to 75psi (was at 100 psi, did this approx 2 months ago). The house is a 2005 and has PEX piping. I have no leaks in the area of the water heater. Not sure what to do. Change out all washers in all the valves? Please help!
Thanks, Alberto