Strange Exhaust sound

I recently bought a 93 gt, and have noticed a distinct difference between exhaust sounds of my old mustang. It has stock headers, and h-pipe, not sure about cat-back. My old 87 5.0 had a tipical kinda smooth sound at idle. My 93 has a metallic sound to it, all most like you can hear the engine parts moving around from the exhaust, its kinda hard to explain, i have no exhaust leaks, and the car is in immaculate shape. The only difference between the 2 is my 87 was a 5 speed, and the 93 is an AOD. I understand that would change the sound during acceleration, but im talking about at idle. Its hard to describe, like "Ka pling ka pling" but very subtle. The car is bone stock and still has the air silencer in place. Just want to know if it could be a sign of a problem, or just my imagination.