It's the flange (where the intermiate pipe bolts to the rear muffler section.) hitting the gas tank shield. I just took a hammer and slightly modified the gas tank shield. No more rattle.

 

Sorry to bump such an old thread, but I just did a search & this is what came up.

I'm getting a rattling after installation of my HKS 272/272 cams & Walbro 255lph fuel pump (this was last year in October), and I've had a rattle ever since.

The rattle only happens at anything above 4,000rpms.

It's not my downpipe, it's not my test pipe, it's not the heat shield above the test pipe (I crawled under the car while it was running & had a friend rev).

As far as I can discern, it's my mid-pipe vibrating/rattling, although what it's rattling against or at is beyond me.

When I take the mid-pipe off and just leave my downpipe & test pipe (both 3" Ultimate-Racing) in place, no rattle.

Can anyone help? It's getting really fustrating

 

I had a mid-pipe rattle with my Buschur exhaust. It was hitting the driveshaft brackets; basically the exhaust sat a little too far to the driver's side toward the driveshaft. I dremmeled down the protruding lip on the brackets and no more rattle. I don't really know why you would an exhaust rattle after camshafts and fuel pump install though Hope this helps, even if it's not on a Greddy.

 

Yes, the exhaust is very loud. If your are still running a cat then you have no idea what loud is yet. Putting a muffler where the cat was will help dramatically in that instance. I have no rattles at all. I have been running this exhaust for 6k miles and it has never rattled. You need to get the car on a lift and look.