How can I stop noisy shower pan?

Hi all. I just moved into a new (for me) 13 year old house. The stall shower in the master bedroom is directly over the family room. Whenever the shower is being used, there is a loud scrunching/squawking noise that can be heard quite clearly (annoyingly) in the family room below whenever the shower-taker moves around. The shower was originally tile walls but a plastic insert was installed over it (prior owner told me so). I am guessing that a replacement plastic shower pan or floor was installed over top of the original shower floor. It sounds to me like the replacement floor was not installed with sufficient support and is rubbing on whatever is underneath. Questions: Do you think this is what is occurring? If so, is there a way to solidify it underneath, perhaps by drilling small holes in from the exterior and injecting expanding foam insulation or maybe by removing the drain and getting in that way? I'm not looking to tear the whole thing out, it just is really loud and annoying in the room below. Any thoughts or ideas would be appreciated! - TSPORT

I think you'd have trouble getting foam in there that didn't blow the slope and the bottom all out of shape. Those things are designed to fit on a flat floor, not a sloped existing shower pan, and that's part of the problem since the middle sits higher than designed. This is out there, but maybe some soupy plaster of paris? The best solution is tear it out, but that will cost some money. If you're willing to do it yourself, less than you think. Check out www.johnbridge.com.

Some shower pans come with a pad which is supposed to be installed underneath it to prevent noise. Others recommend setting the pan in a bed of mortar. If you really want it fixed, you might need to consider a new properly installed shower.