I haven't noticed anything yet. Is it just the back rubbing on the main body of the phone or does it sound like something inside of it? What kind of case you got on it? Is it possible it's the case rubbing up against the phone...kinda like a new dress shoe or something?
Yeah, I noticed this recently also. For me, just a gentle squeeze of the phone's sides will create a squeek.
I don't see this as a big deal (unless it gets much worse).
I wonder if it has to do with the way the Atrix's battery cover comes off and is put back on. I could be way off, but to me, I'd think that would easily cause creaking down the road.