Hi I have a 99 hatch and when hitting 3k to 3.5k rpms it sounds like my exhaust is rattling, but before 3k and after 3.5k the rattle goes away and all I can hear is the normal sound of the car accelerating. My exhaust setup is stock except for the header, but the sound comes from the mid to rear section of the car.

 

Check the heat shields. Usually the culprit.

 

Well the only heat shield I have is one on the b-pipe and it is in the mid to rear section. Never thought of that. I'll take a look.

 

i had a weird rattle on my car @ idle.. turned out to be a AC line near the rad (in the front of the rad) that was "slightly" rubbing.

 

detonation?

 

Ok I checked the heat shields and it can't be that. The sound seems to come from the thick part of the b-pipe (resonator?) and back to the axle-back.

 

Could it be the header making the sound? I do have an aftermarket one.