help, whining sound on new 99 stang

[boister]

I just bought my 99 mustang gt yesterday. Its an mtx, and drives and sounds perfect with only 45K on it. I have one problem with it though, when im driving it and its reving at about 2-3000rpm I hear a whining soung coming either from the motor or tranny. When I look under the hood and i rev it up I cant really hear the sound but when Im in the car I can hear it. The guy at the dealership told me all 5-speed 4.6liter mustangs sound like that. My friend has a ATX stang same year and his dosent make it. I think the guy at the dealer is lying to me. What could this problem be or is it true all 4.6 MTX mustangs whine like that. It almost sounds like a bad ground whine coming through the speakers except thats not the problem..........