They're supposedly ripping the bass out of the spectrum by force. (why you remove the bass to get at a high pitched whine is a question for an electrical engineer). I've had some on for six months as a "temporary fix" because I've been too lazy to actually find the real problem with my install.

Filters on the RCA's aren't a good thing, and if you can avoid them you should... You might do well asking your installer to actually troubleshoot the system, or switching to an installer who will...

Matthew