Does anyone have thoughts on this issue: My 14 Chevy Suburban purchased 3 weeks ago CPO at 28k miles w/still warranty + additionally purchased warranty. On or about 39 MPH to 50 MPH in acceleration and deceleration, there is tremendous vibration. This happens while in local streets to highway. Initially w/stock rims and tires - same issues. And, new 22 inch rim & high end Bridgestone tires - same issues. Took it to the dealer. Inital take in, mechanics have said there is no issues and this is normal. I took it back and requested have service manger test drive with me. He agreed that I have a vibration problem. Replaced Propeller shaft. Ironic that the service dept. have said all is fixed. 5 minutes after I drove off, the same issue occurred. They are having to contact GM engineer to fly in from Detroit to review it. Anyhone with any thoughts on this. The noise is so bad, I am speeding to hit the higher speed 50 MPH + and to slower my vehicle at 38 MPH below, thus creating a dangerous driving habit.

Welcome to the forum Jason!
The good news is that it is under warranty. I hope they can find out whats wrong.
Bad vibes in a 4x4 normally = something is unbalanced or even bent, some where along the line, or not balanced properly.
Of course the question is whats unbalanced?
Since we cant be there to drive it, do you get any feeling if the vibes are coming from a specific area, like more from the front, where it may effect steering or more from rear etc?
Are there any different noises you hear in that 39-50 mph range?

Just to add Jason, do you know what all was inspected before they concluded it was a prop shaft?
I am also wondering if it could be a bad hub/bearing. Does it really sound like roar or?
Have you tried gearing down one gear at the effected speeds, any difference?

either set of tires road force balanced? did they put it on the alignment machine?

Lots of issues with the rear drivelines and some tire issues. Currently the only known cure for the drive shaft is installing a hose clamp on the drive shaft. Luckly your * till under Gms dime. Good luck.

It appears that the noise are coming from the rear. It is a mechenical humming like vibration. I had taken the vehicle to a noise deadening places and they have adv that this is a mechanical issues not a typical noise of a vehicle.

I totaly agree with you. It looks to something to do with "unbalanced" in nature.

The noise coming from, that is acceleratio and decceleration from 39-50 and 50-39 are exact, verbatim, noise of mechanical humming and vibration and no other noises.

Thanks.

Even though this noise may only show when driving under load on ground, I wonder if they would be willing to get it on a lift in gear, using an auto stethoscope and move the stethoscope around in different areas, like firstly on the back side of bearing plates, to see if the can identify a hum or groan for instance that is not right..?? I would assume they checked the hubs / bearings/wheels to be in spec & tight.
They also would be able to observe the rear drive shaft spinning and see if anything is out of round etc...
Of course I would remove the drive shaft, and have the U joints inspected and driveshaft spun & checked to ensure a correct balance.
The GM shop may have a driveshaft balancer machine, and if not a few local drive line places may have one.

I will look into it. Thank yoiu!

Wheel balancing, alignment, replaced with high end tires...........all done. Thank you.