Cub Cadet rtz 50 drive belt comes every time I start my tractor

[Monoxide]

Hello, I'm having trouble with rtz50. The drive belt that powers the the 2 hydrostatic transmissions keeps popping off as soon as I start my tractor. I first thought it was the belt was to loose so I replaced it (what a pain) but that's not it, the new belt pops off as soon as the motor starts running. I have no idea why it's happening, I mowed just last week and parked it. Went to start it today and it popped off. Thanks!

 

[WM75Guy]

Sounds like a pulley is loose or out of alignment. The idler pulley should keep the drive belt tight. Since the drive belt was loose that's where I would look first. Is the idler pulley arm loose where it swivels or has the spring lost it's tension?