Got a 5.2 Durango 2wd. Right around 55-60 mph i get this low resonating drone in the cabin. It stops if i let off the gas, and increases if i step harder. And it kind of goes away at 65ish. Just serviced the rear end myself, didn't see anything wrong, and the oil felt fine rubbed between my fingers, no fine metal or anything. (don't know if this would tell me much though). U-joints seem fine.
Is this just a common sound for these rigs?
or is it possible i need a muffler?
and if I get like a high flow or even a glass-pack, i know it would be louder but do you think it would necessarily resonate in the cabin (it feels like a headachy drone in my skull!) or would it just be louder outside the car?

 

I would suggest paying more attention to the tach and what rpm your truck sits at around the speed you're hearing the drone.
From there you might want to check all the piping, cat and muffler for quality. Hit the cat with a hammer and listen for rattling pieces, which would indicate the need for a new cat. If the muffler or piping is rusting/rotting you might want to consider redoing your exhaust altogether.

If you're considering a performance muffler, a louder system won't always drone, it really depends on what type of muffler you have. When I was looking for a new muffler I spent a few hours on youtube just listening to how certain mufflers sound on the 4.7, or 5.2 in your case.

 

Thanks for the tips!

I found out by turning overdrive off, even shifting to 2nd gear, no change whatsoever, so its not engine rpm dependent (so i suppose not an exhaust drone).

So I figure its somewhere from the Transmission to the wheels.

Then I swerved left and right while in the 'drone zone' : no change again.

So I conclude that it is neither wheel bearings (which pass the wiggle test anyways, but hey...) nor out of balance tires (because I should expect some little change from side to side, even if they were both out of balance).

Seems that the sound MUST be originating in the driveline somewhere between the last bearing on the trans up to the diff itself.

U-joints seem alright, but i'll replace them anyway because they're cheap enough.

trans and diff pinion bearings seem OK? (no play in them...)

How do I tell if the diff is going bad?