Noisy Desktop fans? Maybe just an old CMOS battery.

Several times over the past half a year or so I’ve few issues with my desktop - fans running to fast and therefore noisy, having to reenter the BitLocker key for encryption of Windows drive, RAM profile resetting, and so on. I’ve finally cracked it - the BIOS was getting cleared whenever the PC was disconnected (even just momentarily) from the grid. The weird thing was that several times only some of the settings were lost, not all of them. Nevertheless, new CMOS battery solved it.

(If you’re curious about the BitLocker problem - my motherboard by default has TPM routing disabled. It has to be changed to either fTPM or dedicated TPM. Change in the routing was enough, it wasn’t necessary to retype the encryption key from backup.)