As the subject describes, I have a grinding noise / vibration around 55 to 70 mph. Took it to the dealer today for injector issues, also had them take the truck for a spin, see if they could diagnose. They said "exhaust" and showed me where my exhaust pipe was riding on the cross member where my torsion keys are located. I told them I didn't think that was the issue, but, it was already closing time, so I took my truck home, used some zip ties to temporarily raise the exhaust of the frame, then, took it for a spin. Same issue. So... does anyone else with a 4" exhaust have this issue? From 55 to 70, it's only heard/felt when accelerating. I don't know what else it could be. I'm almost tempted to pull my turbo back kit off and put the stock exhaust system back on the truck, and see if it has anything to do with the aftermarket kit. If it still makes noises, I'll definitely be paying the stealer another visit to prove to them it wasn't the exhaust.

Inspect Your Carrier Bearing Or Your Dirive Line Could Be Out Of Balance
When I Had My Rear Block I Had Carrier Bearing Drop Also And It Help The Drive Line Angle And Pinion Angle. Also You Could Have Play In U Joints Too

I should have posted more details but... I have a fairly new carrier bearing in with a drop bracket due to my blocks. I replaced my u-joints also not too long ago. Truck still made the noise the day I drove it with a new carrier bearing. Truck still made the noise the day I drove it with new u-joints. If it were exhaust related, could harmonics have anything to do with it? Could the harmonics of the exhaust travel through the hangers? I'm trying to think of what all it could be.

What if it's something with my rear differential? If it were, what could it be?

check the u joints- changed mine then 2 weeks later was having simular problems - didnt check the u joint and boom.. i cracked the o/d section of the tranny housing almost off , trans fluid everywhere- it was a mess

If you feel it in the rear of the truck : first i would check the pinion ( remove the rear u joint and check for any play in the pinion move it up and down and in and out) If pinion is good than check the rear axle housing bearings ( remove the rear hub to inspect remove and clean the bearings and check and check the race too) If the both axle bearings are good than i would remove the rear end cover and check for any metal in the oil or broken gears etc.

Exhaust touching any part of frame or body will cause a noise just like you mention. Exhaust needs to be issolated with rubber and not touching directly and needs to be checked under engine torque also. Recently fixed a friends 06 with same issue and exhaust was rubbing on heat shield.

Did you crank torsion bars? I turned torsion bars up to fit 285's when I have heavy load or trailer would get vibration coming from rear end. I addad a leaf spring which gave truck original "rake" stance and vibration is gone. If I have extremely heavy load on dump trailer I will feel a slight vibration but for me problem is fixed with lifting rear end