[92snowmachine]

sounds like the belt has too much slack and is hitting the cover. did you change the water pump, idlers, and tensioner? it's possible to have the belt in time when you turn it by hand but excessive slack when the engine is running that will slap the belt around. i would take the cover back off and run the engine without it to see exactly what is wrong. take another video with the cover off and someone can help you out.