If it's "SYSTEM", that would indicate something running in kernel mode. Obviously that would mean the Windows kernel itself and it's supporting files, kernel-mode (boot-critical) drivers
(like chipset/RAID drivers), and filesystem filter drivers (antivirus/antimalware, 3rd party firewall, etc). Given that Windows on it's own doesn't do this, we can probably safely rule out the Windows kernel and it's drivers. That leaves us with what's left installed on the box - perhaps we can start with that. What (if anything) do you have installed for firewall, antivirus/antimalware, etc. on the computer?