BMWBig6

If these were high-mileage cars, I'd suspect worn commutator bushings (if they even use those in modern vehicles anymore), especially if they only did that at certain fan speeds and not others.

evandro

when i turn my engine on, even on cold start, there is this noise, like a fan noise, humming noise that stays on for ever, until i turn the engine off, i am super worried and please someone help.

Teapotkid

Not sure if this will help but I had a similar problem in my Audi A4 B8... I took the glove box out I turned on the car and went through the various fan speeds, at the same time running my hand around to see could I feel air coming from anywhere.. sure enough I found the filter housing was loose, so i secured it again and 'hey Presto' problem solved, went for a drive and no more annoying whistling... only took me about 25mins from start to finish with a small 8mm socket/ratchet to remove the glove box... best of luck!