On my 2015 Tahoe I had a pretty loud buffeting, turned out to be the black piece of trim on the driver side front door. At highway speeds the wind was pulling it away from the side of the door and acting like a wind scoop. When stopped, it was back where it belongs. I only saw it because when checking the side mirror I happened to catch a glimpse of it flapping out, but even then I barely saw it. I fixed it with 3M tape, and if it comes loose again I plan to replace the piece. This wasn't the first repair attempt either, as someone had daubed in some silicone before to try and glue it into place. The plastic retaining tab on top was broken, probably the original cause. After sticking the piece back on, almost all of the buffeting noise went away. At some point in the future I plan to pull the headliner off and check to see if the rails have separated from the roof skin, if so will epoxy them back into place. While the headliner is down, will be adding sound insulation up there.
On driveline vibration, I had an older Tahoe that I took the driveshaft in for rebalancing. The shop told me that they have to fix a lot of GM driveshafts because the yokes are not always welded in straight, they sometimes get welded in slightly cockeyed. Last time I had to do this it ran about 100 bucks to have a driveshaft rebalanced, if you pull it and take it to them. Further, I've had problems with U-joints with the grease zerk in one of the joint corners splitting, which causes a vibration. Replacing the joint with an Extreme 4x4 U-joint that has the grease zerk in the end of the dust cap helps on this. No idea if this will help on the 2015, I've not actually been under mine yet so I don't know if GM changed how they do the driveshafts on the newer ones.
