It is the Air Charge Pump, I get the same and went to the dealers to ask about the lights dimming too. They said as it draws significant current when it starts up , if the car is idling, it will dim the lights. Mine too will come on for a few short seconds, even 10 mins after it has been started and when I stop at traffic lights within this time period. I do not normally hear it if the car has been running for 15-20 mins +. They said it is normal and notheing to worry about.