Last night, one of my kids got on the treadmill in the basement and as soon as he started running, we heard this WHUMP WHUMP WHUMP noise. Not normal and not good. We stopped the treadmill only to see that the belt had somehow slipped to the side and a tear had emerged . The torn piece was poking up and hitting a plastic piece each time it went around (and getting worse likely each time). So, there goes the treadmill for a little bit until we get the belt replaced (which is on its way).