@ghdprentice I am not sure about noise for two channel amps. I can tell you that with both the amps I have owned that were multiple channel and had ability to mute unused channels, there is a marked difference in sound quality in two channel mode. Typically, multiple channel amps do not sound as good as two channel amps. The exception is when you have the ability to mute the unused channels. I would say in two channel mode the noise is actually reduced over a multichannel amplifier that cannot do this.
The two best sounding multichannel I have owned, and I’ve owned a lot, both had the ability to mute channels.