Question about play in differential

[saltnvinegar6287]

My camaro has a clunk noise in the rear when I change gears and such, so I thought it was my universal joints. I crawled under the car and wiggled the universal joints but they didnt budge or move. The tranny mount is solid, and the torque arm bushing isn't worn. I did notice however, that the pinion shaft which goes into the differential had a small amount of lateral movement. Is this normal, or should this be in there solid. I had a gear swap about a year ago, and they didn't do a good job (whining). Could they have screwed this up too? Thanks