suspicious cyber activity

Do you ever get the feeling that your computer is doing something and trying to hide it from you, even though you are rather sure it isn't infected with malware?

There are times (both on this laptop and my old one, and my work one) where I hear the fan start spinning loudly, even though I haven't been doing anything that should take much processing power.

Then I open Task Manager, and click to see what process is using the most CPU (showing all processes). But then either
...the fan continues spinning loudly for a little while, even though according to Task Mgr the CPU is 95% or more idle
or
...the fan abruptly goes quiet as if it stopped doing whatever it was doing, so that I wouldn't see it listed in Task Mgr.