I think you can sometimes, but it's probably more inside the car than outside. It will make a difference, I'm sure, if you're running slightly raised boost versus significantly higher boost. The S4 (from what I've seen/heard in some video clips) is more audible than the 1.8T, probably because of having twin turbos instead of one. You'll probably hear something, but it won't be nearly as dramatic as a BOV would. However, sound is not worth the cost of an engine

 

lol, everyone wants that stupid bov sound. I don't understand why........It sounds quite annoying if you ask me...........

 

+1^^^^ a sound of a bov is not worth f'ing up your car...besides, in my opinion if i were to hear a bov on an audi, i would not like it. its an audi not a honda

 

^^^with your bt setup your dv will be hella louder then it is now, basically a bov sound