Is the belt correctly tensioned? it is normal for the belt to move a bit on the tensioner, but it shouldn't be hitting anything. Is the tensioner a new one? worth replacing when changing the belt. ALWAYS buy the belt and tensioner from vw, DO NOT buy cheap alternatives!
A quick check to do with tension of the belt - try and turn the belt 90 degrees on the longest run of the belt, and try and move the belt off the cambelt sprocket, it shouldn't move.
If you still got problems then i would suggest stripping all the cam belt out again and checking it all.