Read the forum topic "New Sentra Disappoints". My first indication of a rear axle problem was a rumbling noise from the rear, like I had super snow tires on it. By the time I had it pinned down, the rear tires were hopelessly worn. I then went through months of hassle trying to get the problem fixed by Nissan. My suggestion to you is go to a independent wheel alignment shop (not the dealer) and have the alignment checked. Then go to the dealer, and ask them to tell you if anthing is wrong with the rear alignment. DO NOT let them rotate the tires; this will just hide the problem.