it probly IS a hamster.... shivering for 30 seconds after you turn the AC off.
on a serious note,
what i find weird in this is that when u turn the car off, the blower completely shuts off, it doesnt go into any extra timing by itself. at least mine doesnt
are you sure its not coming from the CD player, or the main radiator fan? i'm more inclined to the CD player cause you mentioned the sound of motors. a bad CD can make that hamster sound as well since its a 6-cd switcher