This was the morning to do something about it.
Crawl under desk, reach behind computer, unplug all 47 cables. Lift computer onto desk. Remove cover.
Carry computer out to garage; vacuum & blow much dust out. Accessible fans spin freely & quietly, except for... the one on the graphics card? That one seems to be seized up right proper, and of course I don't have a spare for that one.
Connect power. Turn on. The fans that do turn seem to do so quietly enough.
Remove fan from graphics card. It's an oddity.
Put everything back together, minus that one fan. Should be OK as long as I'm not using this machine to do intensive graphics. Back under the desk, reconnect all 47 cables, power on.
Now it's back to making fan-in-distress noises, but not as loudly as it had been. Further diagnosis will be required someday soonishly. Also, this seems to imply that the graphics-card fan had failed some time ago and I just hadn't noticed.
Oh, well. Replacement fan & spare ordered from somewhere in the Far East, there seemingly being no localish sources for this type. I suppose I could (the next slot being vacant) kludge on a normal fan, but it doesn't seem necessary. When the replacement arrives, I can install it and also try to identify and replace the noisy one.
Hm. Now the machine's making flying-saucer noises, interspersed with grinding noises. Replacing that fan may be more urgent than I'd thought. Well, at least we're having cool weather, so even with a fan out things probably won't get hot too fast. Unless it's the CPU fan that's going bad.
Maybe I should track it down today.
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