Originally Posted by Kai
A-pipe? WTF is an "A" pipe?"
The "B" pipe is what would be called a downpipe on the turbo, the thing that connects the manifold to the rest of the exhaust system (generally, a cat converter.)
The exhaust manifold in 3rd gen integras are double-walled, and first half of the manifold (The A section, closer to the block) has a failure that the internal welds start to fail and it develops a resonance around the 3.3-3.5K RPM range. Sounds like absolute ASS, almost like you have a piece of metal stuck in the exhuast manifold that's being knocked around super fast.
Happened to me... swapped out the header for an aftermarket one, and poof, no more noise.