Thanks for the tips! For me the solution was even more simple, so I thought it might be nice to share it here:
I had a similar issue with lagspikes, where they would appear constantly every 5 seconds or so. After troubleshooting for a while, the problem was a wireless usb dongle for my keyboard - unplugged it and the lagspikes were gone!
So make sure to check that option as well if you are encountering similiar behaviour.