I have the EXACT same behavior with my VZN100 MK V's and assumed they are all that way. I noticed it reduced the noise when the driver test buttons are pushed, but never even thought about operating it that way full time. The risk of screwing up and pushing a bias button simultaneously seems too great to me.
I previously had Reimer Teton GS's which were 95db sensitivity and it was really intrusive with them on quiet passages. I didn't worry about it too much since I had VSM-MX's on order and after talking with Jud a couple of times I decided it was normal and I'd just have to live with it. With both my TSM-MX's and the VSM-MX's, the reduced sensitivity helped, but the noise/hum is definitely still there.
These amps otherwise sound so terrific. Do I need to just get over it and enjoy them?
Tom