Strange Explorer Behavior

WIndows 2000 PRO Svc Pk 2. HP Vectra.

User started noticing strange behavior in Explorer. When the Explorer window is open, there is a steady “flicker” like a heart beat. The lower portion of the Explorer tree, like Network Places on down, flashes steadily, about every 1 second. There is a corrosponding CPU jump of 15% with every flash. Most irritating is when the user attmpts to use a drop down menu to select a drive or folder, the “flash” closes it before he can pick the drive or folder. When Explorer is closed, the behavior stops.

No new apps or system changes (to my knowledge!) were added to this PC before this started.

Has anyone seen this before? Any ideas?

Thanks!