melabyad

hello, i was just wondering what the problem could be.... i have a 2000 gs400 when i start the car there is a hummming noise while it is in park- i can hear it more inside the car than outside, when i am driving there is no noise but if i am at a stop light and then push gas to go the humming noise comes back and goes away, mostley i can hear it while it is in park????? thank you