Multiple squealing toilets

[Momto3]

I'm hoping someone has some suggestions for me about a toilet issue we are having. Our upstairs bathroom toilet has been squealing when flushed. My husband replaced the fill valve inside that toilet but that didn't seem to fix the problem. We've noticed recently that another toilet is doing the same thing. You can't hear the squealing in the actual bathroom but we hear the noise in our bedroom which is directly below the upstairs bathroom and next to the main floor bathroom. Any suggestions about other things we could try to remedy this problem? Thanks for any ideas you have!