I replaced the rear tire, tightened the drive belt and I have a problem. When I push the Spyder forward, I can hear a steady, gentle knocking in the rear wheel. It sounds like the belt is too tight. But I loosened it and there is no change and the belt cannot be loosened any more. When I reverse the Spyder, nothing knocks. When I lifted the rear wheel and turned it, the knocking stopped when I loosened the belt. When I put it on the ground, it knocks again. Any ideas? Has anyone had a similar experience?