Let me explain, it's don't happen exactly during change gear.
It's actually happens when u actually clutch in, release
accelerator, then change gear. So the key point is the accelerator.
When u throttle, the turbo kick in, charging lots of pressure of
air into yr engine, mixing with los of fuel, causing huge
combustion, causing yr RPM to raise fast, then when u need to lower
yr speed during cornering or throttle off, the high pressure of air
between the turbocharger and the engine have to be release to
somewhere, so that somewhere is actually the Blow Off Valve, this
reduces turbo lags, then that's when u hear the huge amount of air
being forced out, causing the sound Psss....
