[Charlie-141 FE]

My neighbor recently bought a 1250. He replaced the rear engine mounts with neoprene bushings bought at Napa auto. The engine runs great at idle but when the throttle is increased to max there is a bad vibration that seems to be coming from the rear part of the tractor. He said the vibration was there before replacement but it was not quite as bad as now. The drive shaft was removed to install a new fan, but shaft appears to be straight and true when running. One blade broke off the fan during installation, Any suggestions? Also one other question it is really easy to move the tractor with the engine off... just push or pull and the rear wheels roll, Is that normal for a hydro?