Both the actual *nix load average and the CPU time over process lifetime average done by KOReader mean nothing really interesting.
You'll notice I said "when idle". Of course the average is not null, work has to be done sometime to display stuff
.
Get a shell, look at htop, and you'll see that pretty much zilch happens when idle, no matter the software being used. Same with perf counters.
The Forma may be a different device, but it's built on a very similar board than the Clara.
The thing they do have in common is that the screen is driven by a TFT. That those can whine in certain conditions is not new. I've seen it happen on laptops, and on desktop monitors as well, especially when displaying certain patterns.