I have a 07 SS with 28k on it. When im driving it i hear a noise when im at a certian speed and when i let go of the gas pedel. At first i thought it was my exhaust but thats not it. It sounds like something is rattling but when i give it a little gas it goes away, then a minuet later it comes back.. its irrating. Everything is stock on my car, and i still have my powertrain warranty. anyone is familier with this problem or know what it is?