I wish that I had better news, but my 2016 Genesis 3.8 AWD is back at the dealership, for the 6th time, to fix this vibration. They have replaced the propeller shaft and adjusted the driveline angle with shims 4 times, maybe 5. They will add a shim, then take it away, call it fixed only for the problem to present itself immediately after driving out of the dealership and driving 30-35 mph. They are frustrated with me, but it is not me, but the car that has the problem. I didn't design it or build it, but I did pay for it. What good is the powertrain warranty if Hyundai can't actually fix the problems with it?
Anyhow, don't let anyone tell you that it is the tires, a flat spot, a bent
rim or something to do with anything other than powertrain. It is a driveline problem, and here is proof:
The stock tires on the 3.8 are P245/45R18's with a circumference of 83.8 inches. So for every single revolution of your tires, your car will move ahead about 83.8 inches. My car's vibration is MOST pronounced at 33 MPH, but quite noticeable between 30 and 36, especially when cold. 33 MPH converted to inches per second is 580.8 (1 MPH = 17.6 inches per second). 580.8 in./sec divided by 83.8 in. (tire circumference) = 6.93, or approximately 7 rotations per second...let's call this Hz for the purpose of diagnosing the vibration. That means if you have a bent
rim or flat spot on your tire, you will feel about 7 pulses per second at 33 MPH or a frequency of 7 Hz. The vibration that we experience is faster than that. How much faster? Let me suggest it is about 4 times faster, or about 28 cycles per second or about 28 Hz. Now you are getting closer to a frequency that you can feel AND hear or sense as a buffeting or low rumble, similar to a low bass note from a woofer. The (healthy) human ear can sense frequencies above 20 Hz and can sense it in other ways other than just hearing; in our gut, or in our case, in our butt. But why 4 times faster? Guess what the gear ratio is from your drive shaft to your rear diff? It is 3.91 to 1. So the vibration, flutter, buffeting (whatever you call it) that you are feeling AND hearing is happening at much higher a frequency that anything that your tires would produce at that speed. It's something connected to the driveshaft...something spinning at about 30 revs/sec. or 1800 RPM , if it is a first order vibration.
I explained this to the service department and they gave me a funny look. Have to see today if that is good funny or bad funny. They did take the car in to look at it for the 6th time, after all. Hyundai engineers know what the problem is. I am sure of it. But they are hoping that we do not complain and "just live with it." I won't be doing that. And this will probably be the last Hyundai product I buy, unless they step up and fix this annoyance. They say that this car is a Mercedes killer? Hardly. Step up, Hyundai.