Knocking noise...possibly solved

Just to let everyone know that was reading my previous threads about the knocking/rattling noise. Took it to dealer today and went on a nice test drive. The tech said he thinks its a loose heat shield on the exhaust. I'm going to crawl underneath it again this weekend and take a look. I'll let you know if that's it. Hope so!

Off topic, but on an aftermarket x-pipe system with cats....are their heat shields, or any problems with not having heat shields....or are they not needed since the cats are typically in a different location?

Thanks!

Nope, just a test drive which he heard the noise. Before having him doing anymore...I'm gonna take a better look at it myself and see if I can take care of it.

Its a very strange noise. At idle, sounds like air rushing...inside the car, it almost sounds like the heat/ac is on with the air rushing thru the vents, but it's not. Sitting in neutral w/ clutch in and out, it will rattle at various RPM's....but its pretty reliable to do it at about 3-3.5k. Also rattles while driving. Strangely, it will not do it with the hood up....and I know someone said there's a lot of ambient noise, which I understand, but if I can pick out the rattle on the interstate next to a semi, I should be able to hear it with the hood open, especially when its pretty loud with the hood closed.

I crawled underneath and I'm assuming the heat shields the tech was referring to are the small metal plates attached directly on top of the cat's. Almost a double layer of metal there. Do the stock GT's have two cats on each side (I know...cumb question)? On my 04....there's the larger shape that is almost vertical by the manifold connection, then another...longer shape that is horizontal closer to the crossover. Which is the actual cat? Anyways, I've poked and pulled and knocked, and none of this stuff seems lose, and the dust shields don't seem to be bent or close to anything to be making contact, unless they're rattling near where they are attached.

I'm thinking possible BS too. Car is still under warranty, just don't know if its something that's loose and I don't want to get charged for them taking the time to find something, say its not covered, fix it...then not really fix it, and keep taking it back, etc. etc. I hope to find the prob myself, but I'm not very good at diagnosing.

Thanks guys!