What kind of valves?
If the valve packing on a conventional valve is bad the valve stem can vibrate causing a squeeling noise.

Repacking the valve (Teflon packing is the best) usually solves the problem.

The valves? I have a moen shower faucet set. Not sure if this is what you mean by kind of valves. What is the "valve packing?"

Can you walk me through what to do? DH has pipe wrenches, teflon tape etc and is quite handy but not sure how to solve this/what to buy.

Thank you for answering. My children will be so happy not to take a "scarey" shower.

Found the solution online and thought I'd share with anyone is the same boat--the tub spout diverter wasn't sealing properly. If I put my hand tightly over the spout while the shower was running, the noise stopped. I noticed the tub was also still dripping water when the shower was running. So I adjusted the pull up plug to be tighter and voila, no more noise. Free and works. Can't beat that!

Does it start to squeel when you pull on the diverter to run shower? Probably is a bad diverter and you can purchase your brand diverter spout from hardware store and replace.

This post is 9 years old. I think it's safe to say they've figured it out.

I saw that....just thought anyone else NOW looking due to same problem would benefit. thks