I have not had a chance to get under ours yet, the wife has me so busy working on everything else around here...lol If there is a weld broken on a heat shield, I would bet that's where it is coming from. Could be wrong, buuuut. Anyway, to attempt to check to see if that IS it, go get either some RTV sealer, or JB weld, or something similar to that and cover the broken weld with it. It will not fix it really, just quiet it down so you can figure out if that is where the sound is coming from.