LA105 Transmission belt issues

good morning all (or afternoon),
I bought a used LA105 from a gentleman prior to last season and I am just now running into some issues. I mowed with the tractor last season and had no issues. This season, an excessive 'rattle' has developed in the transmission belt area. I have replaced the belt and the two small idle pulley's to no avail. The belt appears to be extremely loose and shakes around when the brake pedal is disengaged. If I apply a small amount of pressure onto the pedal, the noise stops. I checked the front pully (double pully on engine) and everything is tight without any movement. The two idle pulley's are new so I checked the transaxle pulley and it has quite a bit of movement in it (side to side wobble) - is this supposed to be the case? Only other parts that I could replace is the brake linkage and the extension spring that attaches to the idle pulley plate. I have looked online at the parts website and cannot seemt to find the shaft or transaxle pulley for purchase. Any help or insight will be greatly appreciated.

Derrick