once a while when i'm stopped at a traffic light, i can feel/hear some motor kick in for a few seconds and then it stops. when the motor kicks in, my dash cluster lights dim for a split second too.

what is this motor and what does it do? it must be drawing lots of current to dim the cluster lights

__________________
Current cars:
2001 MB E55 AMG
2003 Honda S2000
2000 Honda CRV

Gone but not forgotten:
2004 BMW 325i 5sp sport
1999 BMW 540i sport
1997 MB E420
1995 BMW M3 coupe