2002 Chevy Impala

My Impala just started making humming/whining noises when I backed out from a parking space today. As I accelerated from the parking lot I could still here it but as I went faster it seemed to fade. I have not changed my fuel pump, fuel filter or spark plugs since I have owned the car for the past 4 years. My oil change company recently did an oil change, checked all of my fluids and changed the serpentine belt. Thanks for any ideas you may have so I can guess how much I might need to spend to fix this problem.