I was doing my oil change and when the engine was running i was underneath and noticed a distinct hissing noise under the car (not audible from the top) coming from the drivers side turbo area. first thoughts are wastegate vacuum leak but i'm not 100% certain the N75 valve is open and would allow a leak at idle, that turbo also leaks oil into the intercooler and associated hoses so i am a little suspect. Second thought was maybe its just the sound of hydralic fluid going to or from the transmission (tiptronic).

so my question is, has anyone noticed this sound before? is it normal (transmission causing the noise) or should i isolate the wastegate line and see if it holds pressure?