recently my PC very often occurs to be very slow. It happens especially during video playing (e.g. netflix, but also local files), that the PC just stops doing anything, the mouse moves extremely slow, but often the situation relaxes after 1 or 2 minutes.
When I check the resources tab of system monitor I see a CPU usage of 100% on all of my 4 cores. But when I check the process list and try to kill the highest CPU user, I just don't find anything. It just shows some 10% usage (2 or 3 processes), but they don't sum up to 100% at all.
Does anybody know, what happens here? How can I find the problematic process? Could it be some malware, that hides from the process list? Or could it be some system feature?
Thanks for your help in advance :)
BTW: I'm using Ubuntu 16.04 LTS with Unity