I have a shower that squeals when I lift the plunger to convert the water flow from the bathtub faucet to the shower head. You have posted info on this in the past and refer the reader to use an imbedded link to view a video I think, however the information has been removed.

More details Please, Brand name of the shower valve? One handle or two knobs? Is the diverter on the spout? Where's the noise coming from? The spout? The shower valve? The shower head? Did any of the posts below help at all? Back to you, Tom