Mystery noise

When I put the key in the ignition on my bus; not turning the key far enough to crank the starter motor, the gauges all go to maximum and an electric motor starts. All the switches on the console are off. I have no idea what this motor is doing. Suggestions have been made about it being a brake booster though why that should start when the handbrake is on I don't know. I asked the question on a forum and predictably the Peanut Gallery said it was the Lithium Drive unit (from Star Trek). Any ideas, anybody?