Originally Posted by HDDP
Not to say that this is the problem with his car, but mine turned-out to be some sort of harmonics that vibrated the heat shield above the muffler during very specific speeds... It took me a few weeks to figure it out... Just another opinion...
Its called resonance (natural vibration). If the differential or any other component produces the same frequency sound as that of the natural frequency of the heat shield, the heat shield will vibrate causing / adding to the buzzing. It is possible.