Very unnerving sounds coming from my stang...please help!

Within the past few days, I started hearing some strange noises from underneath the hood of my car. It sounds almost like a metallic vibration or rattling (it is fairly loud). When we popped the hood, it almost sounded like it was coming from INSIDE the engine, almost. When underneath the car, you can hear it's coming from up above. The sound stops under braking, and sometimes just isn't there. For example, we started it up earlier, didn't hear it, gave it a little gas, and it started right up. It's almost like a squeeking, but it sounds metallic. It's really hard to explain. We took the serpentine belt off, to make sure it wasn't the smog pump or something, which was my first assumption. Much to my dismay, the sound was still there.

If it makes any difference, I just installed BBK o/r hpipes about a week ago. If anybody can help me out, that'd be great. Whatever the sound it, it doesn't sound very good at ALL. The weird thing, is there is other noticable effects. The car performs and acts 100% normal. Anyways, thanks in advance.

Logan

All brackets seem to be intact, the hpipe seems firmly placed. No out of the ordinary vibration.

In case it matters, the car is an aod. I called a friend and talked to him about it, he said it sounds like it could be the torque converter going out.

Logan