Mine were Flowmaster 40s with an 18" extension on the outlets that extended 2 inches past the rockers at the tip of the door edge. The mufflers were mounted to a 12" flex bent at 45degree angle. Factory manifolds and pipes cut Just before they merged. The whole thing was less than 4 feet from the cylinders. LOUD. When I added the extensions the interior resonance was reduced by at least 60% while retaining the "Hey look at that car!" sound. It was worse at 35mph than any other range.
Since I installed the SIDEPIPES I haven't had to worry about any of this mess. Thats right I said SIDEPIPES.