Alex is right...driveshaft isn't moving in park.
...and not to argue with you, but it's very hard to figure out where a sound is coming from. If it's definitely not under the hood (you should listen with a stethoscope or hose), then the only other things I can think of is fuel pump. There's nothing else moving when you're in park.
Try filling up the car above 1/2 full and see if that quiets the noise down (if you happen to be low on fuel)...
Have you Mangofied your car yet?
Thursday, August 6, 8 p.m. The Comedy Cove--595 Morris Ave. Springfield NJ Reservations: 973 376-3840
Sunday, August 30, 8 p.m. Tierney's Tavern, Montclair, NJ
A recent set.