after eliminating alot of possible culprits, i finally found what is rattling at low rpms. Its the heat shield that is on the engine where the 02 sensor is. It seems that the bottom fastener has just poked right through it. Any advice on this? its very hard to reach down there and i cant find anything to tighten it to. I was thinking if im able to get the fastener out i could put a big washer on there, other then that im stumped.