In my guest bathroom, there is a single handle shower faucet, likely an early Delta or American Standard scald-free ('monitor') that occasionally screams/whistles when being operated.
It doesn't leak, and I believe the scald-proof temperature control works adequately. Anyone have any experience with this issue? Do I need to replace it, or try a seal/spring kit?
High velocity flow through a restricted opening connected to a resonance chamber causes whistling. Things you might try other than modifying the valve:
Install a flow restrictor at the shower head. It only needs to restrict the water a little to change the dynamics of the flow through the valve. If you start with one that restricts the flow so much it is annoying, you can usually enlarge the opening in it with a drill. Of course, if you enlarge the restriction too much then you will be back where you started.
Check system water pressure. If it is above 60psi, then consider installing a pressure reducing valve on the system.
