I've been experiencing a drone/resonance in my '92 ( see other posts) and I can't tell whether it's exhaust related or engine mount related or maybe somethig-else related. Anyway, from reading other posts regarding exhaust drone with some aftermarket mufflers, it appears that this might be what I'm experiencing. I have an original, oem exhaust sytem on the car and , based upon a cursory visual examination all appears to be be tight ( although I can't see the manifolds). If this is exhaust drone, what might cause this with a stock exhaust?