My 3.0 litre awd automatic makes a strange whistling noise if I hold it in 3rd gear and keep on accelerating, sounds like a turbo spooling up or a supercharger, I thought it could be a massive air leak at high revs, have no codes, no missing in the engine , she runs like a dream and can redline it until the limiter kicks in.What could be causing this sound?

 

Bad driving belt pulley? there are 3(?) pulleys, compressor, alternator. Get stethoscope and listen each pulley.