Sounds like belt stretch. Tighten the two bolts, one on either side, at the tail end of your treadmill. Besure to tighten these bolts evenly and alternating side to side. This is also how you can fix an alignment problem, tightening just one side will move your belt over one way. Continue to pull the tail roller back until the belt is fairly tight, turn the machine on and run it in the very slow speed. Now slowly tweek each side until belt is running center, careful not to over tighten. Hope this helps. Happy treadmilling!
joe domingo
September 2009