This suggests to me that there must be something going on in the wireing to the bias controls that is injecting noise into the amps... something that I will have to talk with Jud about.... It can well be that RFI is sneaking in via the system that connects the amp to the built in LCD meter... loading it by pushing one of the bias buttons down may give the noise somewhere to go or prevents it from making its way in.
Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison