Your eyes can deceive you, don't trust them.

I'm pretty sure that a rider this past Sunday had a bent hanger, but I heard it more than I saw it. It was only after I could ride behind him for a couple minutes that I could get a good look. It's still hard for me to tell when a bike is on the floor or in a stand, especially if the RD is bent just enough to add noise or shift funkiness but not so bad that anyone could spot it from across the street.