Hi, on my 156 v6 (2002 version) the subwoofer of the Bose system makes something rattle when there is too much bass. It is on the right hand / rear side. Is it correct that there is only a speaker/subwoofer on the right/rear ? The left speaker grill looks and sounds empty. Is this a general problem with an easy solution or will I have to strip the rear shelf to find what is making the rattling noise?