The belt was damaged. Not 'broken', but there was a small spot where the belt was 'stretched', exposing the underlying metal. Each time this spot passed around the tensioning pulley, it would not immediately seat properly in the grooves on the wheel, causing the 'knocking' sound. I sent pictures of the belt to Elite, and they sent out a replacement belt and pulley kit for free. All told, it was ~ 1 week from the time I contacted Elite customer service about it until it was fixed and back to normal.
+Morgan Friel There are (at least) 2 Tinicum Townships in PA. One in upper Bucks County (where I was) and one in Delaware County (where I'm guessing you live).
