Recently started hearing a high pitch whining in shower. It's walk-in shower with single hot/cold knob. I removed shower head and still hear the noise (although not as loud). Not present with just cold but begins as I turn the knob to hotter water. I haven't tried adjusting the pressure, but the water pressure in our entire house is not very good. Neighbors report low pressure as well, so I don't think it could be a problem with pressure too high.

Any suggestions? Thanks.