This may be non subaru related but recently I sat my friend's Evo 8. Runs on Apexi pod filter which is the same as mine.

Upon release of accelerator, it lets of a flutter sound, "chu chu chu chu"

I have the same intake as him however mine doesn't make such noises.

Any clues what causes these noises ?

That noise is what every trev in his VL Turbo aims to get

I believe its unused air getting blown back thru the filter. Well thats my non mechanical explanation. I am more than likely wrong

Air being blown back into the spinning turbo blades. Taking your blow off valve off will make the noise the best

By the way he's using a 100% atmosphere vented one. Might experiment by tightening my Stealth BOV's spring tension. Its running kinda loose at the moment.

Your mates car will have a frontmount intercooler. The more the air has to travel, the longer apart it flutters. as the guys said its air bouncing back and foward down the intercooler pipes.

Cool cheers. Was reading up on impreza forums and apparently this isn't good for high boost.

Check your CD, mine does the same noise, but sound like this … “cha cha cha cha” and only happens when the CD is playing some Latin music.

right ...

No it isn't..

what causes it is having a blow of valve on to hard, or not at all, and its the turbo trying to spin down against what is now stagnent air, and its actually the turbo stuttering, for lack of a better word, down in RPM very suddenly, its not overly good for the turbos longevity as it will cause it damage over time if its very severe...

got nothing to do with air bouncing around the cooler or pipes..

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Jesus Built my car, Its a love affair, Mainly Jesus and my hotrod

Doesn't a turbosmart veeport 2 bov make a noise like that when you change gear or let go of the accelerator???

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