G’day Andrew,
We just picked our Q5 55 up a week or so ago and I notice the same high pitched whining noise, though I suspect mine is from the electric motor.
I’ve not noticed it when in pure combustion mode.
it is very loud and I seem to be able to replicate it when the engine is under load, I.e up a hill, higher gear acceleration etc.
have you had any luck with Audi?