Whistling sound

fdiphill

Hello,

I have a shower with a single handle mixing valve, (american standard 20+ years old), my issue is when the hadle is in the hot (extreme left) or cold (extreme right) positions the pressure drops to a trickle in both the tub spout and shower head. But if the handle is centered for warm water the pressure is fine. What would cause the pressure to drop and also when the water is in either extreme positions I hear a whistle comming from the pipes.


Thanks,
fdiphill