I dunno whats up with my '01 S3 but if I give it some beans it feels like the turbo just gives up, the dump valve is usually really loud but after some thrashing it'll give out one long blast of air, then it feels like the car is running less than half the boost. So I stop, turn the engine off turn it back on and it's all good. It's got me very confused. Has this ever happened to anyone before? I'm thinking dodgy dump valve? maybe sticking open?