Brakes were squealing, but still hear a little roar
I didn't have time to get the Bonneville up in the garage, so I took it by one of the mechanics today. The back brakes apparently were rubbing the backing plate and/or drum, because they did see metal shavings in the brake dust. After cleaning that up now hopefully I won't have brake noise for a while.
I'm wondering if it might be a wheel bearing, too, making the noise, but you would think it would be a more consistent noise. I'll keep you posted! Thanks for your help.