I picked up a pair of Pioneer BS22 bookshelves a while back, and the overall tonality quality is very good. The trouble is that at moderately high volumes for certain frequencies, they begin to show some type of internal vibration or crackling sound which is audible and unpleasant. (Both speakers.) I've been using them as computer speakers and for a lot of the time they're okay. However I've started using them as nearfield monitors (primarily for guitar) and in that situation the vibrations are significantly worse and very noticeable, for whatever reason. Has anyone else encountered this issue? Is there something I can do to fix it, or should I move on to some other speakers? It's not clear to me whether this is a defect (in which case I can complain to Pioneer about warranty) since it affects both speakers.