i need help figuring out this weird noise from my exhaust . i cant tell if it's a leak or if it just sounds like that . i recently welded on a new cat converter . and it sounds like a thin piece of metal (like a nail or screw) that rattles inside of the exhaust piping around the cat while i am driving, but it doesnt make the sounds when i put it in neutral or when i am at idle . its a h23 in an accord if that helps any .

 

Sounds like an exhaust rattle not a leak. I would say check all your heat shields under your car and make sure everything is tightened down and all hangers are on/installed properly.

 

it could be the cat shield. the welds on my cat sheild broke recently and i had to fix it by putting a worm style clamp around it and tightening the hell out of it.