Snapper 10/28 soft start tranny vibration

[lee]

The vibration makes the whole mower shake and is worst in 5th gear. You can feel and hear the vibration. I lifted the back of the mower so that both tires are off the ground and stopped each tire one at a time to see if the vibration changed and it did not. So I'm thinking it's not axle bushings. Engine mounting bolts are tight. I put a new soft start hub, clutch disc and liner on thinking that this might cure the vibration but no luck. I'm thinking the problem might be inside the differential or chain case. Maybe one of the chains is rubbing against the case? Other than the vibration the mower drives ok. Any ideas?