Audiolab 7000A pre mode

I have a question for any tech heads out there: When I switch my Audiolab 7000A to pre mode, I hear a bit of a click which I always assumes was the power amp section being switched off internally via relay or something. If this is true, why does the amp still get just as warm on top? I always thought it was the main mosfet/transistor (or whatever they call them these days) componentry emitting the heat. I mainly want to know if the amp is using less power in pre mode. Can anyone explain to this dope?