you should always be checking the coolant level on a cool car as this is the only way to properly tell where the levels are at
as far as the coolant level dropping after being overfilled its normal, the expansion tank will release some fluid if its been overfilled
the audible whine I also get the same thing on some start ups, I haven't looked into what it actually is but a couple of other mk6 GTIs ive seen do the same thing
Polo GTI
T-Roc R
Tiguan R
When your car is cold set your level to the middle seam of the tank. This will when car is hot/ pressurised make the level appear to be approx max. This ensures you have plenty of coolant to not bring on the low level light when car is at operating temp.
As said if worried about loss of coolant mark the level and monitor over a period of time.
The whine noise is nothing to worry about. All of the tsi engines have made this noise from day one from my experience.
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