Yeap, totally agree with you. It 's the vacuum pump, it has a tiny piston in it that makes all this noise. I somehow managed to minimize the sound a bit by putting a plastic connector to the vac hose that makes its inner diameter a tiny bit smaller. The noise is still there, but not so annoying: P
Nice
Could you please send a picture how your plastic connector looks? And where you get the parts?
Do you now feel a difference in boost pressure or power if you make the diameter of that connector smaller?