I had a similar problem with another turbocharged car (Alpine-Renault GT V6Turbo). It turned out to be the hose which connects the high pressure (output) side of the turbo to the intercooler which was not well fastened. Only under high boost pressure (full throttle) it started leaking and made a trumpet like noise audible inside and outside the car. It happened because some mechanic forgot to tighten things well enough.

Total longshot: Anything in the intake path (cold air intake

or air box)? A lot of air flows in under full boost and I

imagine if you had something in the path there would be enough

air flow to possibly make it "whistle".

(I've noticed my T5 has more induction noise then exhaust

noise under full throttle but no real whines to speak of.)

I also have a turbo and the car whined loudly, but only in cold weather for almost 30 minutes of driving (Whined louder the harder you pressed). It turned out to be the belt tensioner for the serpentine belt. It was just replaced yesterday and when I started up this morning no loud whining noise. I know this isn't exactly what you described, but it's something to consider.

And JohnB is right, all turbos make that siren type whine noise, I remember when I first started driving the car in 1994, I kept looking for the cops in my rear view!!

Hope this help

Scott

sounds like std siren-like noise from turbocharger.