Mine's exactly the same, John. Seems to be at its loudest when the air is cold and the car has had about five minutes to get halfway warmed-up. Other days, it's hardly noticeable. Didn't experience this with my previous turbo'd motor - it had a fairly consistent-sounding high-pitched whistle (distinct from the spin-cycle sound of the WRX turbo).
Also, mine doesn't boost totally consistently. Seems to need a few blasts on every drive before it begins to boost smoothly and fully - especially after a week of pottering back and forward to work. I'm told that this is 'ECU learning', but I'm yet to be fully convinced - I do get a fair bit of 'wastegate chatter' (or 'boost solenoid ticking' - not exactly sure of the source). I always wait until it's warmed up before I give it a proper belt, BTW.