My truck has had a quiet rattle that you can hear under the body of the truck (even when its just idling), and it has been like that for a long time. Recently, it has gotten a little louder, and I was wondering if anyone might know what this is? I thought maybe it might be a belt or a pulley? Let me know if you guys know anything. Thanks.

 

Could be a loose heat shield on one of the cats. If it was the belt or pully then you would have more of a squeeky sound. Not a rattle.

 

thanks.