why do some cars / engines do it and not others? When i had my 1.8T passat, which is the 1.8t 20v found in say, the golf mk4, I drilled (wak) the airbox and the car made a nice roar on acceleration and you could hear the BOV when you let off...then when you wanted you just drive normally and hear nothing. When i first got my a3 2.0 tfsi I thought...ok great will do the same and guess what? it made no difference. No roar, no bov noise. Just quiet. I'm not bothered now as the car (see below) got put back to standard airbox and I'm gonna sell it later this year. I am just wondering...why? Why no noise? Even with a big cone they don't sound very good compared to the 1.8T which had character. My old golf vr6 sounded AMAZING with a few holes drilled in the airbox as did my 330ci. here's a pic I took of my car..had it about 2 years now and it's been great, but on to 3.0 tdi ownership soon as i far prefer low down torque now.