My '90 535i has exhaust problems (106,000 original miles). There's a shudder in the exhaust system when accelerating from a stop that keeps getting worse. Now it's making a rattling sound when I decelerate and the exhaust system seems to be clogged up because it's starting to hiss/whistle after the engine has warmed up. I realize this can be very dangerous and am tempted replace the entire exhaust system, but am confused as to how many parts there are. There is a front, center and rear muffler, as well as a catalytic converter? Would it be wise to replace everything? Is there any where you might recommend where I can order the entire system and related parts? to Any suggestions? Input is greatly appreciated. Thanks.