Check the "runout"on the sprocket shafts.This is easy to do,make a loop of stiff wire and attach to a conveniently close bolt hole,bend wire so it is just touches machined centre of shaft and turn through 360deg several times.You will immediately see if there is any "runout".

Shafts do bend and they do break.

I have been having the same problem as you are discribing.

I have repaired my cam belt failure and the engine runs fine at low rev's.

But when the rev's are increased the cam belt tensioner ' tab ' bends and it makes a rattling noise. ( as if its being over loaded )

I wonder if had any ideas of what could be causing this ?