Silent computer
Turns out the weird irregular fan-revving in my computer case wasn't a buggy onboard thermostat fan voltage varying thingy like I thought. I'd been cooking up ideas to spoof the onboard plug into thinking a fan was attached to it (BIOS won't let the thing boot if there's nothing on the plug) and power the thing directly off the power supply. But I finally actually opened the case and looked. The CPU fan was constant. The noise was coming from... the video card fan? Well poop, that's easy. It's not the kind of fan that's worth cleaning and oiling—I've been down that road, and you just end up cleaning and oiling it again in a couple of weeks, rinse and repeat. It was gummy and slow and needed to die.

I went into my stores and fished out an old 486 heatsink and fan. I yoinked the fan, clipped and stripped some wires, soldered the old fan's connector on (man, I haven't soldered anything in years), zip-tied it onto the old fan's metal cage, plugged it in, and hey, silent computer for the first time in six months.

Six months? Why did you wait so long to take care of this?

Shush.