I have the premium DSP sound system CD changer etc...and I replaced the rear speakers with a pair of Boston Acoustics. I did this because I thought these were the source of the vibrations I would hear at high volume. The guys at the Good Guys electronics store didn't know what the hell they were talking about. The installer didn't even know that the grills pop off!!! He told me they would have to do MAJOR work to change the speakers. Please don't waste your time with these unqualified "good guys". I asked them if the system has a subwoofer and they said "NO". I figured that the vibrating was from the heavy bass so maybe it was coming from a subwoofer. Then I come home and see this link http://www.nextmill.net/bmw540/ which clearly shows that I have 2 subwoofers. I want to get rid of the rattling vibrating sound that I hear that I believe is coming from the subwoofers. What should I do? Can you change the subs and get better ones? Can you disconnect the subs altogether? Anyone out there who has modified their sound system in a 540 please respond. BMW DSP Woofer System