Iknow this is the wrong section but the street/strip section seems to get more knowledgeable people (and more in general)so i'm hoping I can get some help....I also posted this in general tech and exhaust. Does this sound normal...it mainly does it after first gear and when slightly accelerating. I can rev it out of gear and it sounds great...dunno.

http://www.youtube.com/watch?v=HOy1cm5CcXs8 seconds into the vid it does it

 

not a mechanic here or anything, but it sounds fine...if i were to make an educated guess, i would say it is a protective plate beneath the catallitic converter, which is to protect it from damge from below...the plate is held alot of the time by bolts going from the chassie down, four in a square configuration, and a plates is attached, the plate can rattle on the cattalitic converter itself or just rattle around...