This was helpful, in my electronic professional opinion that chirping is a two (or three) part issue:
1. The firmware update has caused the processor(s) to run a little warmer and possibly combined with a different threshold being introduced to the temp/cooling system. (When it engages or not) has the fans running more often.
2. As high quality the FAS products are, these little cooling fans are all made in places where quality control can be questionable and it appears some of the fans on units are not as mechanically stable and are physically rubbing the fan housing due to oscillation imbalance, especially at higher speeds. Since the fans are now running more the likelihood of finding some units with less than perfect fans is being revealed.
disclaimer:
…then again I could be totally wrong!