So it's not a scan or vrdb right?

Not necessarily. The on-access scanner message shows, indeed, files scanned by the on-access scanner.

VRDB has its own icon that is being animated during the generation. Scheduled scans have no tray icon.

And if 1 and 2 are only intermittent then I would not expect the i/o counters to just continously climb.

Intermittent but constant. I’d say the mdb file is accessed approximately once a second (go blame MS :P)

They are doing it fast but they never stop.

Fast? Shouldn’t be more than a couple of reads per second.
And these are serviced from the cache anyway… :-\