With mine it was my fmic hose joiners werent tight enough, (maybe over time had loosened themselves due to constant expansion and contraction maybe) Anyway it was worse where they connect at the throttle body(inlet). I spoke to John (Dude) and he recommended I pressurise the system which i did ,(cheers DUDE) and I could here the air pi$$ing out. Also had a split hose at the back of the engine at the top I think its called egbv vsv . So tightened all intercooler hose joints and replaced the vacuum pipe and ran spot on after that with no nasty noises.