Electrical issues...common?

I get weird sounds out of my amp due to electrical happenstances. If I switch the ceiling fan off in my room the amp pops. Today I took the amp to a friend's place, and he had a fan plugged in across the room out of a different outlet, and the whole time my amp was making weird noises. He turned the fan off and the same sort of popping noise came out of the amp. I plug first into a Furman SS-6B power conditioner/EMI RFI noise filter, which I thought was supposed to kill buzzes and whatnot.

Sounds like you may have a bad power conditioner. The electrical current in your house most likely has all kinds of voltage irregularities in it which cause your amp to pop and make weird sounds, especially with things like your buddy turning on a fan. I do lots of home recording and before I got a good surge protector, if my Air Conditioner kicked on my monitors would shoot out the loudest pop you have ever heard! Hums and pops are caused by LOTS of other things than just your house's electricity. Could be a pedal in your board or a problem with your pedalboard's powersupply (if you have one). The Furman should clean most of it up and the fact that it is not makes me think there is a problem with it. Take the amp over to a friends house or some other location off your grid (hopefully one that has regulated power). If the problem goes away, you know that something is up with your neighborhoods/houses power grid.

Just because the fan is on another outlet does not mean that it's not interfering. That other outlet is MOST likely on the same circuit.