I've got a Craftsman 917.273080 with 46 in mower deck that has started wobbling/vibrating as soon as the electric clutch is engaged. I thought it was out of balance blades but I replaced them and it still wobbles. I've also replaced all idler pulleys. There is no obvious reason for this wobble, everything seems tight. The drive belt and center idler pulley are jumping around like crazy making the whole deck shake. I can mow with it but it sounds and feels like the deck is going to come apart it is vibrating so bad. What's causing my problem.