If you are concerned about the wheel-drive slipping, it's best to diagnose the problem before you commit to replacing the belts. Pushing the belt tensioner is the first step, and inspecting the belt, and the drive pulley on the engine's Power Take Off shaft is the second step. If the belt has been bottoming in the pulley, it will be visible on the pulley: the metal at the bottom of the pulley will be shiny. If it has been slipping due to bottoming, the bottom of the belt will be shiny, and there may be heat cracks along the length of the belt. If the sides of the belt are shiny, but the bottom isn't, it is likely to be a tensioner problem. However remember that tensioner problems usually result in poor forward drive, but good reverse drive.
It is also possible to have squealing sounds due to the forward clutch being glazed. This happens when people run the machine slowly with the engine running full speed.
