I used to run with the GReddy type S bov, today I put my friend's BOV(apexi) to my car, and I can't hear any sound too ,any ideas ? I checked all the vacuum hosts ,and I didn't find any leak........

 

it's probably plumbed back into the inlet (which it should be if u still have the air flow meter). and if u still have the stock air box, that won't help either. if u use a pod style filter you'll get plenty of noise. but really do you want that sound??? it attracts cops