Could we assosiate this drone to resonance frequency? I could well associate mafia's problem to similar background to mine, as i have got the "Drone" syndrome with mine. mainly around the 80-85 it would start, and reach around full drone around 100-110 around that area, where it is quite loud. this would be assosiated with 5th gear, so around that rev range it does it, 4th gear would be similar to around the 60 mark, but no where near as loud as 5th at the above speeds.
On the theory of the flexible hanging mounts. Im not too sure if they would be greatly assisting the problem no matter how many you put in or have, as the metal itself would still have its natural RF properties, and would still occur. Changing the characteristics of the metal will help, Stainless vs Mild, Stainless having that tinny sound while Mild having the drone. The only way I can see to minimize the drone, is to either change restriction value of the system, ie: mufflers, resonators etc. and change to a better steel compound mild to stainless/titanium.
Cheeers