92 sedan deville strange exhaust/motor noise

I have a 92 sedan deville w/ 100,000 miles on it,The engine runs great,but, Ive always had a strange gurgling, or knocking sound coming from the firewall area of the car while accelerating. At first I thought it was a plugged converter, Midas said it was ok. I know the car has a stainless steel exhaust system on it, I was wondering if it is double walled pipe, could it possibly be collapsed. Ive also been told that this is an inherent characteristic of the car, I kind of doubt the validity of that claim. any thoughts??????????