Is it a laptop or a desktop?
For differences in BIOS and Ubuntu, it could be reading different sensors. One may be for the motherboard and the other CPU. Myself, I'm easily confused knowing what's what.
For differences in OS, it could be CPU frequency scaling or just the kernel drivers for your hardware. I.e. idle devices are still drawing power or CPU is in "performance" mode all the time.
I'm not that familiar with config files for fans and sensors, but if it's "back to normal" when booting to a live session (off a DVD/USB) from power off then some leftover config on your actual installation must be telling the kernel to crank up the performance / fans until the next power down. In which case, a fresh install easiest way out to clear of any residue configs.
For further reading - Arch Wiki has quite the documentation on fan speed control: