I would also like to share my experiences with this issue:
Bought one pair from Thomann January of this year, unfortunately both speakers had exhibited this problem, so I was forced to return them. Sadly I did not note the serial numbers.
Learned about the new hardware revision from this thread, so I thought I'd order another pair from a local store this month, but they still had the coil whine present, so it was another quick return. In both cases only the power cable was attached.
Serial number was: IUD04-61YFAD**-*****
And on the bottom of the speakers there was a sticker with 220303** which probably indicates the manufacturing date? But I am not sure how to read that so it might be something completely different, so take that with a grain of salt.
Edit: The second pair I ordered came with the firmware that allows for the 80 Hz low cutoff setting, so it had to have been at least version 1.2.0.