Please repeat watching "processes" in action, this time using Process Explorer. Expand the processes tree ro maximium (click all "+" signs), watch and report heavy users. Process Explorer will give us a finer resolution.
Do you have a firewall installed and running? Do you have any remote connection program?
From what I see up to this point I can't be sure what is going on but I repeat my observation that your computer is definitely not as it should be. Please report HDTune and Process Explorer result. If by then I cannnot pinpoint the problem then I think we must make sure that your computer is malware free. That will be done in the malware forum of G2G.