1. Either a knackered Actuator or more likely badly adjusted.
2. Forget the dump valve. Leave it off!
3. Whistle? It's a Turbo, not Louis Armstrong. Anyway, if the Actuator is badly adjusted as per number 1 in this list, then you probably won't be making any boost.
4. Everyone will tell you that their RST is 200+bhp, but in truth very few are. Get it looked at by a proper tuner.