Vibration at constant speeds - solved

I bought my Kia Stinger 2019 (MY20) last September in Sydney (dealer demo, 7000 km), since then I noticed the following issue:

When cruising at about 60 km/h (or about 40 mph) I would feel and hear a low frequency noise and vibration which was very annoying. The cabin resonates at this low frequency with every bump or slam of the traction control (which happens all the time when making turns) anyway so it took me a few weeks to realize it was not road noise. At higher speeds it gets higher pitched but never goes away. At first I thought it was tire balance/flat spotting issues or even the rotors. I took it to the dealerships about this issue several times, I ended up balancing the wheels, changing the diff oil, machining the rotors and changing the tires, all of which didn't help. The noise occurs whether the car is in drive, neutral or coasting.

Eventually the dealership tried replacing the diff under warranty and returned it to me clearly without road testing it - that didn't work either, in fact it made the noise and vibration a dozen times worse and basically the car was undriveable. By this stage even the dealership guys couldn't pretend not to notice it anymore. When they took it back they spent a few days changing out parts from a donor car they had sitting on the lot until they eventually found the tail shaft (driveshaft) was the culprit.

After having this component replaced, it is like driving a whole new vehicle (but still more low pitch thuds and road noise than your average car - perhaps the body is just taught and well insulated like a drum?). I no longer have the noise when driving under any scenario. I'm hoping there's no way it can come back (perhaps from the way it's mated to the diff, as changing the diff made the original shaft vibrate worse?).

I just thought to post this issue since I've seen similar problems being alluded to before but never found a definite fix on this forum since I started looking last year.