I also experienced the same problem. On boost, or near it, my BOV was separating from the intercooler and letting air out. I couldn't figure it out for about a week. A friend of mine had me rev the engine and found that the BOV was separating on let off. It make a weird sound kind of like a howl.
Oh, I forgot to tighten the BOV down and consequently the bottom screw of the BOV fell off!