I get a "clonk" sound when pedalling heavily in a low gear, for instance when going up hill. It only happens when I'm on one of the larger (bottom 5) cogs on the cassette.
It appears to be something to do with the rear mech. I have a new chain, a newish cassette (100 miles or so) and new front cranks. My rear mech is a three year old XT long cage with new (LX) jockey wheels.
So far I've:
-Fiddled like crazy with the indexing. The shifting is fine, but the clonking remains
-Checked the pawls on my rear hub (Hope II). They are all fine and springy.
-Checked for stiff chain links. None.
-Checked the cassette for damage - none. Does not look worn.
-Checked my frame for cracks. None that I can see and it is only a week old anyway.
This is driving me crazy!