Having a similar issue out of the blue... I have read other places that it might be the battery "sweiiing"... My MBP is not 2 years old and no longer under warranty... Should have sprung for the Apple Care, but thanks for posting here. Was going to pop it open tonight anyway, but I will try the screw under the case first, and then see if I still need to pop it open...
May need a n we battery soon if it is "swelling" though... I'll report back later tonight.