Brought it into a car dealership today for an oil change, and the first thing i told em was about it only happening at startup for a few seconds, and at 1400 rpms when driving, and first thing they said was heat shield. They checked the heat shield and said it was good. Again i cant really find the rattle since it only happens when in drive at 1400 rpm, cant just stick it on jacks and pin point it, any more suggestions, its really starting to bug me

 

Check the knock sensor counts while at that RPM. If they are increasing, chances are the timing chain tensioner is to blame. GM has a TSB on this issue. The RPM listed isn't exact and can occur at lower RPMs. The KS counts will let you know if it is internal to the engine or not. Something to check anyway.

 

well its not comeing from the engine bay, its somewhere from about the cat back towards about the muffler, i know for sure its there somewhere, the mechanic was a guy i know whos not the best at looking over cars and started the job 2 days ago, so who knows he could of over looked a crack somewhere