I cant figure out what is making this noise but its kind of annoying does anyone know what it could be? It started when I first had the new muffler put in I think but Im not really sure. I believe it happens in third gear because it will sound fine at the same rpm's until it shifts. The car sometimes also has a rumble/vibration niose when you shift into reverse. Your help is greatly appreciated, thanks.

 

make sure the muffler isnt hitting anything underneath and that the exhause is all clear and has room to move. the sound u hear could possibly be rumming or whaat not on the chassie. reason i say this is how the body twists or shifts when you put it into reverse or when its low rpm in third. i mave a vibration when i get on mine and it stays there till i let of and get back on it. and thats my problem is the twist of the chassie and the way it plants its-self

 

If the buzzing started right after you put the muffler on, either the muffler or a pipe are touching something.

 

I took it in to a different shop after the first guys screwed it up and they straightened everything out and went back through to make sure nothing was touching. The body shift theory seems like the most logical explanation. I may have a fix for this though I'm taking it into a speed shop and they're going to put the car on a lift and hang weights from the corners that need adjusting and then weld in my sub-frame connectors while the car is twisted the right amount.