I was at a party this weekend and a friend of mine introduced me to this guy who wanted to look at my car. He had sold his mustang a while back and was telling me about how much he missed it. Thats when he asked me to pop the hood so of course i did. Then he says if you take the hose going into the back of the plenum (the piece with the mustang on it right?) off and tells me to start the car up. I did and the exhaust sounded kinda cool and there was a little bit of whine coming from the engine. I assume the whine was air coming out through the hose. Anyway I just wanted to know if anyone else has ever done this or if its bad for the engine? The guy said he used to drive around like that so i dont know.