Another side note:
at one point when I started it cold (one of the many times during my test) and the fan didn't run, I actually blew a puff of breath into the fan and it started running. That sort of reinforced my hypothesis that once the fan actually gets enough voltage to start running, it can run at less than 3 volts.
the fan on my GK 1001RB-II is like that. Sometimes, if the amp is hot and the fan still hasn't come on, if I stick a screwdriver in the fan blades and give it a push, it will start spinning. I've been told this is a symptom of a faulty fan...

I did notice a bit of noise when I remove a cable when muted.