Turbo: Troubleshoot Owl Sound on Acceleration
On your Turbo-charged car, there are a few special pieces that N/A cars do not have, a Blow Off Valve or BOV is one of them. Your BOV acts as a pressure release valve for your car. When your turbos produce pressure (boost), it flows into your combustion chamber. When you let off the gas the Throttle Body plate closes. There is still pressure trapped in your lines leading from the turbos to your Throttle Body. This is where the BOV comes into play. Instead of the pressure flowing back into your turbo and causing backspin or compressor surge (your turbos violently start to spin backward...VERY BAD) your BOV opens and the boost is released through this valve. (That is the whoosh sound) When you are accelerating and you hear a hooting sound, it usually means that your BOV is leaking (releasing pressure when it should be closed) There are two possible fixes. One is to replace the BOV. It is located coming off the Y-pipe and connecting back to your T-pipe just after your air flow sensor.
An alternate fix that may work is to flip the inlet and outlet around. This way, instead of boost pressure trying to push the valve open, it helps seal it tighter. This will help stop the leak (as noted by the hooting sound going away), there does not appear to be any side effects (no turbo surge), and you can hear the normal operating sound of the BOV a little better.