Originally Posted by sydney
Sounds hosed.Get a replacement.
Quick and to the point. And probably wrong.
Start with the pedals, then the cranks. Make sure its all nice and tight (have your LBS do it if you are not inclined). Have em check the fit/tightness of the bottom bracket. Since it happens while standing, we can elimnate the old chestnut of the seat post.
Could still be a hosed bracket, but at least you don't go rushing to swap something that may not be the problem.
I though my newly aquired (but 14 yr old) Phil Woods bracket had gone south, it made such a racket. Turned out that the cups had just worked loose.