I was raising this topic several times among others, but've never posted how the problem exactly sounds like.
Maybe someone had the same issue and got it solved. Sadly my mech doesn't want to cooperate.
- got new exhaust manifold gasket & got it planned (don't mind it - it repaired one rocket-whistle at cold start, but not this one)
- got ordered two check-valves (evap/brake booster) and will try it on
Circumstances when it happens:
- Accelerate more than 30% throttle
- It does not happen only in the turbo RPM's range, little hiss also happens when in neutral (First rec.)
- The best environment to hear is tunnel or driving next to metal barrier (Second rec.)
- You won't hear the hiss when standing opposite to the car's hood.
- Hiss comes from rear of the engine/exhaust. You have to lie down to hear the problem.
- When you release the throttle there is a sound like remaining pressure exits (any valve?)
First recording is at idle, cold start, when I can also hear the hiss.
Second recording is running at 3rd gear, near metal barrier.
1 - https://drive.google.com/file/d/1OGl...ew?usp=sharing
2 - https://drive.google.com/file/d/15wq...ew?usp=sharing