what does task manager show as running that is requiring more than 1-3% of resources (when browser is closed)....
you might try a brief Malwarebytes Antimalware scan, just to make sure no nefarious processes are mining crypto-currency, etc., on your rig...
see if this process can be suspended or terminated when running Process Explorer as admin..
https://docs.microsoft.com/en-us/sysinternals/downloads/process-explorer
and, see if the process in question has legit signature, no Virus Total hits, etc...; you can also examine or jump to it's file location...