Chances are your blower motor is dying. They get very dirty over time. So dirty, the dirt drys out the bearings until the blower cage freezes up. The whinning is dry bearings. Usually a cold motor will squeal. As the engine heat warms the motor up, the cage may turn to some degree.

These motors are accessed from the engine compartment by removing(or at least setting aside) the wiper assembly.
If you have a couple of hours and are somewhat handy in the DIY department take the motor out and replace with new/rebuilt/used. Or if your brushes are in fairly good shape, clean the dirt out and shoot some WD into the bearings.

I have had better luck finding 190E and 190D blower motors in better than good shape for replacement. Not very lucky with the 300E models.
Perhaps someone here may be of help if you chose to replace the motor.
Unfortunately the 190E 190D blowers are smaller than the 300E. Not interchangable.

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Selling used Mercedes parts on Ebay...always changing...
cdplayer51 take a look!
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