nostr:npub1z2qdmfzhs2uwg8kmsh37xavt2hq48gch63e787ggd3s6mt8waxgsxu3yuf When you say "no obvious reason", do utilities like "top" or a desktop CPU monitor widget show low CPU % usage? I had an Ubuntu box that would thrash the CPU because of some problem with the CUPS print service.
Discussion
nostr:npub1xt7wmvtpswlza54mku4a04xtwdrw9xx4p48cppn4d4nrt9w2xzasg0aztg Indeed ... "top" and "xload" have shown virtually zero CPU usage.
Latest news is that I've installed TLP and the fans have spun down. So the symptom of spinning fans has gone ... I still don't know the original cause.