Deep Humming sound

This is on a 2000 Wagon with the 24V engine and 78K miles. While driving there is a deep humming sound from the engine compartment. I thought it maybe wheel bearings. Checked the wheel bearing and they seemed OK. Put it in neutral and it didn't go away. It didn't change when turning either way. When I parked the car I got the humming at 3K rpm while in park. Any ideas as to what to check first? I hope that it isn't the torque converter.

Are you sure it is coming out of engine compartment and not frrom fuel pump?