I have a new t/a with only 300 miles on it now. I have gotten into the throttle a bit, up to 3 grand or so a couple of times just to stretch her legs, and fluctuate the RPM's for engine break in. The exhuast sounded "poppy" and the car felt doggish. I just thought maybe it was my expectations were higher than the cars ability. Well tonight, I got into it a bit more and took it up to 4 grand or so, then I heard a mellow pop, and it felt like a turbo car hitting its powerband. It was night and day. The exhuast sounded more evened out and more of a rumble vs a popping sounding exhuast. Which brings me to this question, could one of those butterfly valves been stuck and it took more pressure to get it to start working properly? Or is this normal?