We've got a similar issue, but, our "whine" and "drone" is on an '08 Sprinter 3500 chassis.
When talking with some different differential experts, when they found out it was a "Florida RV" possibly sitting for quite a while, bells went off and corresponding sounds emanated from the phone.....as in, "ahhhh !"
Turns out, there were two issues with Sprinters :
#1) When Mercedes owned Dodge, as it was told to me, they imported the Sprinters un assembled, assembled them here, and they could possibly sit around for a while before being shipped on the docks.
#2) If it's an RV in a humid climate, the differential sits "half in -half out" of the precious bath tub that is the differential, with oil/fluid that protects it only covering half of the metal. The other half corrodes causing the characteristic "whine-pause-whine-pause...etc.." rotational noise.
The drone ? no idea. But, it occurs exactly at 55 mph which on rural Ontario highways is a perfect speed. Arghh !!!
The other nasty thing that I was told is that you can replace the whole thing and STILL have the exact same recurring problem. It turns out that differentials are made differently today than they used to be. The expert explained it but I can't remember the difference. There used to be a mitigating design which is no longer used....maybe much in the same way that transmissions these days are sealed !!! imho, this is ridiculous.
2009 Fleetwood Icon 24A-Sprinter Diesel