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.

Do you notice being down on power at all?
I am not sure if this is your problem, but I will share what happened to my 86 that was making a similar noise. The left rear cat has somehow broken off a piece of the honeycomb inside it and this resulted in a metallic pinging as well as greatly reduced performance due to the restriction. I dropped the cat back and checked for flow out of both pipes and found the driver side had significantly less than than the passenger's side. After checking further with a flashlight, I could see the broken piece. If it was one of the front cats, it would have been impossible to find with a flashlight, but the flow decrease would have helped find it anyway. It was still the stock h-pipe, so I switched to a Bassani X and was all set. Another option would have been to cut out the old cat and weld in a new one, but with the restriction of the stock h-pipe w/4 cats, the best thing to do is swap it out. Let me know what you find and I will check back on this post in a day or so.

Does it have a smooth idle? I had a friend with a '74 chevy truck (pos) that had a crazy metallic exhaust noise that ended up being a bent exhaust valve that ended up falling in the cylinder and destroying the bore, so it basically killed the engine. (this was of course after he wrapped the heck out of it going up a dirt hill several times and driving it home). It's probably not what it is, though. the exhaust systems of both vehicles should be identical, so it's anyones guess what it is without more info. Good luck