I think its becuase the side panels are snapped on and not glued so there is a little play to be expected. I wonder if you took them off and used a q tip with a little wd40 if that would cure the squeak.
I've had mine for a couple of days now and both sides have a little play. It's noticeable because it is right where you hold it while using it. Who is going to be the first person to take the sides off? If you could take them off and apply something on the inside (tape) to "snug" them up a little the looseness would go away.
I got my phone last Tuesday and guess what?! Both sides squeak. They didn't before. The right side squeaks/flexes both under and above the buttons and the left side between the usb port and the convenience key as well as above the usb. It's annoying and it seems to be getting worse. *bummer*
I've had my 8800 for over a week now and the squeaking hasn't gotten any worse. If it gets bad though I may swap the BB out with another, but as of now it doesn't bother me. But remember, if the BlackBerry is a squeakin', don't come a peakin'!
I was having squeaking and slight movement problems on mine as well. I just put my new Invisible Shield (full body) on the phone today. Oddly enough, the slight mistakes I made in applying the shield seem to have tightened up some of the looseness that was contributing to the squeaking. For instance, the Cingular branded piece under the keyboard and the battery door, both of which previously shifted a bit, no longer do so. The side pieces of the shield, which could have been cut better, have made the sides of the phone a bit sturdier. It's not perfect, but it's something to consider, as the shield also seems to be a great way of preventing scratches.
"Boy, I got vision, and the rest of the world wears bifocals."