Recently I swapped out my stock downpipe for a perrin DP. Prior to the swap there was this odd wooshing/ratchet like noise emanating from the turbo/up-pipe area where the DP mates to the turbo (at least that's the best place i can pin point it).
Car is 2008 wrx hatch with perrin turbo back exhaust stage 2 cobb map. no other mods.
I figured it might work itself out when i swapped out DPs however the sound pretty much stayed, i thought it was possibly a bad cat in the stock DP.
The story so far:
When there's a cold start, it only makes the swoosh/rattle between 2.5-3.5k RPMs by that point it either stops or I can no longer make it out. I can only hear it with the windows down. I'm unable to recreate the noise when I am parked just revving the engine. The other noticeable feature of my new sound is that the car almost feels like it will stall out when coming to a complete stop and with my foot engaging the clutch.
I've taken it to the dealer to check and make sure there is no leak within the turbo and lines, everything came back fine. I've been under the car, all of the heat shields that follow the exhaust back are secure and there's clearance between the exhaust pipe and the shield, so I can confidently rule that out.
The odd thing is when the car has been driven for about 30-45 min the sound seems to dull and isn't as noticeable.
Could it be an issue with a heatshield on the exhaust manifold? The almost stalling out makes me think there's an issue with the MAF sensor but i cannot see how that would effect this noise.