Why does my OS hangs for less than a second?

I use Ubuntu 18.04 with kernel 4.15.0-39-generic.

My system:

  • Intel® Core™ i7-4710HQ CPU @ 2.50GHz × 8
  • 16 GB of RAM
  • NVIDIA 860M
  • Disk is WDC WD10S21X-24R1BT0-SSHD-8GB (03.01A01)

My system hangs for 0.3s to 0.7 second every (mean) 7 minutes. It affects audio, video, program and even CPU interrupts.

My disk S.M.A.R.T. status is OK.

Whenever this happens i get a spike in the CPU chart of System monitor. The freeze is always followed by the CPU3 spike and is always close to 60% of usage.

There is normally no intensive use and it still happens at the same rate.