McAfee"s scan32.exe runs itself

Hi,
I have McAfee VirusScan 8 Enterprise but the problem is:

Although there are no schedued tasks, sometimes when computer is idle
or i'm doing smth, scan32.exe which is McAfee's on-demand scan module,
begins running at the background with a lot of CPU use and excessive
HDD activity. No dialog boxes appear. I've updated and completed last
scan properly.

But what is the reason of self-running of scan32.exe?

Thank you