I wouldn't recommend going after the axle if you offroad.
I have my magnapack dumped basically under the backseat and it drones a lot around 2,000rpm not bad any other time, however 2K is cruising rpm.
WSI has the same setup as I do, but about 1-2 feet further back, still in front of the axle and dumped. He says the drone isn't nearly as bad as mine.
I don't mind it, but most of my passengers do. The drone (along with the boat-like suspension) actually puts my girlfriend to sleep. So... it's hard to say whether you'll hate the drone or not.