If you grease all of the brake components, pads, rotors etc, the noise should go away. Unfortunately so will your braking!

I had a noise that could be described as a swishing on my 190E. It turned out to be the dust shields rubbing on the rotors. The high points were obvious when I removed the rotor. A bit of careful straightening and alignment sorted this out.

A slightly dragging caliper could also be the culprit as you suspect. So might loose bearings if this allows the rotor to wobble slightly.

I think I would take off the caliper and the rotor and give everthing a good clean, looking for rubbing marks, and reassemble.

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Cheers, Neil