ABS light on, rumbling, light off

Hey there,
My girlfriend recently purchased a 2001 Montana. The ABS light has been on quite a bit but we've noticed that shortly after starting engine and starting to move, there is a brief rumbling from behind the dash on the left and then the ABS light goes out. I assume it's the ABS system engaging. Should I worry about this right away?

As long as the light goes off shortly after start-up don't worry about the light. If it fails to go off then you will want to have it checked by a mechanic with an ABS capable scanner.

... there is a brief rumbling from behind the dash on the left and then the ABS light goes out. I assume it's the ABS system engaging.
Absolutely