Originally Posted by TheWeatherman

Sounds like the fuel pump to me. You can tell because when you dog it a bit, and the electrical system is strained, it temporarily lowers in pitch. I've heard fuel pumps in a lot of my cars I've owned, and it sounds almost exactly the same as all of the others. My vote... Fuel pump. Other noises... a bit of interference coming through the stereo system. I've also heard this in other cars that I've owned.