Should I just turn the volumn down on the preamp before I shut the power amp off?
Yep.... And if the preamp has a mute feature, mute the preamp before turning off the power amp.
Post back with your results.
My Bryston 7B SST monoblocks make a small noise when shut off. It sounds like a switch being opened. It's not bothersome.
Assuming the source is not playing, the volume on the preamp should not make any difference since there is no signal flowing through it.
You could send an email to Classe to see what they have to say. My guess is that it's nothing to be concerned about.
I would conclude amps differ in their behavior when powering off. Case in point: I have had 2 amps from Belles, the first was the HotRod 150. It never cared about sequence when powering off.---The 150a ref. I now have requires the pre off first---or change to an unused input,by remote,in my case.---If it ain't music,I don't want my amp reproducing it.