Same issue here. Bummer, since they sound amazing.
Received a white MTM pair fresh from Modena 3 days ago. Both speakers have a high pitched coil whine emanating from the rear, marginally louder on one. It's like instant tinnitus, quite distracting. I have the same on my Belkin Boost charging station when nothing is charging. When you power the MTMs off, the pitch slowly rises to dog whistle frequency over the course of 2.5 seconds, then silence. Never saw this mentioned in the several YouTube reviews I watched, but then again they were all done by Americans who live in a 120 volt universe. We have 240v in Sweden.
Updating to the latest firmware made no difference. Not sure what to do here? Returning them for replacements seems hit and miss, as 2 out of 2 speakers I received have this issue, and I'm guessing nobody in the warehouse is going to plug in and test replacement units until they find two hiss-free ones...?