Try Disable the MemoryDiagnostics task in Task Scheduler. It is set to run whenever the machine is idle for 10m, and to stop as soon as the machine is no longer idle. And the task is also hidden by the way.
This was my issue for the CPU fan constantly spinning up for no apparent reason while the PC is unattended. Sorry but I was not paying attention to the RAM usage, only the CPU usage. It would always calm itself down immediately after I would touch the mouse or keyboard.