2003ish Cannondale six13, all Ultegra.
Frequently, but not always, when I'm coasting at a fast pace, usually down a hill, the bike will start making this hideous screeching/grinding noise. It is silenced if I rotate the pedals a bit, but might start up again immediately. I'm reasonably certain it's coming from the bottom bracket.
My questions are:
If it is the bottom bracket, why would it be making this sound? Can the existing one be serviced to fix this?
If it can't be serviced, should I just get a new bottom bracket and install it, or could it be something else?
Since I cannot reproduce this off the bike, what should I look for if I take things apart?