I was trying to find causes/solutions to the creaking sound coming from the shower pan. This forum has provided valuable information. If only I knew prior to the installation...

Here's the situation: my shower pan has been installed without a mortar bed. While the pan is mostly rigid, it gives the occasion creaking sound. Although the ideal solution would be to tear it all out and have it redone, I am trying to see if there are other approaches.

There is a crawlspace underneath the bathroom. My initial thought is to inject foam between the subfloor and the shower pan, allowing for the foam to provide support to the shower pan and minimize movement. My questions are:

1. Would this be an acceptable approach?
2. Is there such a foam spray which will cure rigid, be able to expand and fill the space, and have minimal compressibility after curing?

Please also provide any other recommendation on how I can provide additional support to the shower pan. Thanks in advance for your help!