Originally Posted by
DiabloScott
If the chainstay is cracked, it ought to show itself with a little force applied from the side - just hold the bike up with the brakes on and sort of step on the chainstay or BB laterally and vertically (like we used to do for evaluating how flexy a frame was) and listen for crunchy noises. OP's bike is aluminum so it should be obvious.
And yeah, near the dropout and the BB are the most suspect places, unless there's damage from a kickstand or something.
I was thinking that perhaps there might be a a sleeve or inserted part similar to a steel frame lug or dropout where one piece is sliding deeper into the other with chain tension, then being pulled back out with the brake. The flex test wouldn't catch that. (I wouldn't expect the failures the stress test would readily catch to behave with the "clunk" the OP describes. My chainstay failures didn't.)
Ben