Got a Astra-G Z20LET, it makes a whistling sound when you're on part throttle (about 1/2 to 3/4) so I'm thinking its related to the blow off of unused air. It doesn't make this sound when you're driving without boosting too much or when you're FLOORING it. I've checked the boost lines at the back of the engine and they seem intact.
Also I should mention I've got a very agressive exhaust (freeflow) and intake system (1.9 debaffled airbox and Vectra intake) as well as a FMIC. Turbo and map are standard.
Car goes perfectly and there are no error codes.
Anyone else experience such a noise on part throttle?