It could be the bearings but then the entire diff would be wobbling. Check the 4 screws on the spur gear that hold it to the diff case because they could have came loose. This will require you to take the entire diff out of the buggy so if you aren't familure with these buggies just pay attention to how you take it apart and get the instuctions if you still have them. Only other possibility is that you actually bent the spur gear. I never heard of that happening though and I don't see how it could happen.