I was suspecting leaking BOV valve so I removed it (hoses plugged).
Surprisingly whenever I lift throttle when on-boost I still get the sound...

Suggestions?


it's a 97 impreza turbo

 

The sound you hear is the built up pressure being released when you close the throttle. With an atmospheric BOV it is just released into the air and you can hear it alot more. With a recirc it is released back into the inlet before the compressor, if you have an induction kit on you may still hear the noise slightly. If you take the valve off completly and block up the holes, the air goes back through the compressor and out of your airfilter. As it has gone through the compressor the noise sounds "chopped" up. This is compressor stall or surge, quite alot of people wrongly call this "wastegate chatter".

 

interesting, I watched some youtube movies showing surge and I must admit that was it

 

Its a squirrel mincer