I just installed a set of hooker comp headers and after cutting out the old exhaust had a new flowmaster exhaust system installed properly. Sounds great, problem is once the car gets hot, and car is in gear and usually at lower rpms I notice a rattling/knocking sort of sound coming from near the driveshaft area (i'm assuming, not 100% sure). Any ideas on what this might be? Until it gets hot the car performs great, but once hot it knocks/rattles at lower rpms, thanks in advance for any info!

 

Did you look under the car to see if the pipes are close to anything that it may be rattling up against? I can't see that from here!

 

I have looked a little bit,but not extensively. my assumption is that it's definitely hitting something, but wasn't sure if this was a known problem. I haven't had a chance to lift it up and get a real good look. on the upside, man does the car sound great now!

 

wanted to update.... Found the noise. When the exhaust got hot enough and the pipes expanded some it was just enough to vibrate against the "X" Brace underneath the driveshaft. pulled it off and it went away, will be installing the hotchkis "X" brace that is stronger and allows more clearance for larger exhaust pipes.