I'm having an interesting experience with my disc brakes. Sometimes, for no easily apparent reason, they often make a kind of scraping sound. If I re-adjust the wheel and quick release, it sometimes goes away--or sometimes it turns into a kind of cat-like howl. Then if I go through the process of undoing the quick release, putting the wheel back in the dropout and tightening the quick release, the sound may go away. There must be a more intelligent way to solve this than by my half-assed trial and error method. By the way, they are Magura Julie's. In the stopping power department, they've been fine.
Thanks for your help!