hmmm... i had a similar thing about a week ago. after closer inspection i realized it was coming from behind the glove box. it was something with the a/c blower, it would rattle when it was turned on, went away when i turned it off. this was driving me crazy, especially under the blazing south florida sun!! i thought it might have something to do with the fact that i cleaned out the cabin filter recently, and i was going to check it out, but the noise went away after about a day or so. is this what you're talking about? if not, it may just be the passy seat jittering a bit, mine always does at idle. hope this helps