I have read your posts but I'm a little confused:
1. how can I find the version of u-boot? Updating kernel implies update u-boot ? (sorry, but I'm a newbie in linux environment)
2. hdd noise and Power-Off_Retract_Count are You sure that are event indipendent? I ask this because I have 2 WD60EFRX, I have disabled the parking head timer whit wdidle utility, but the noise of parking head was less sharp then noise that I'll get when turnoff nas (I don't know if this happens also on reboot or not): seems that here is something that screeches
. So, for my opinion, the problem is that the head should be parked only when turnoff the system (before shut down the power to hdd) and the sharp noise is related to this
3. can You share an audio record of the noise?
I don't know if this happens also for hdd enclousere usb, but the best thing is parking head and turn-off hdd before power off for both sata hdd and usb hdd.