If it's like mine, it seems to be comng from the catalytic converter. Once u hear the noise if u crawl under your car and hold the cat) looks like another muffler but right in the middle of ur car) the noise stops. I don't know if there is something loose in the cat, but it's definately coming from there. If u have the windows down and the car is under load u can also hear it then. Haven't taken mine in yet.