The prior owner (or someone) must have fiddled with the stock sound system in my 1991 560 SEC. Maybe there was an after market CD player installed or removed during the transfer of ownership. Anyway, the system is extremely bass heavy with most of the bass coming from the door speakers. Adjusting the tone controls on the stock Becker barely make it listenable and that's with full treble, no bass. I think they got some wiring screwed up somewhere. Radio/Casette (no CD) work fine otherwise. Any thoughts on what to check?

Thanks,
J.Chip