Started having vibration at speed a couple of months ago. Thought it was the tires, they were old and over 50K on them. Got the tires replaced. Still vibrating. Re-balanced twice, still vibrating. Moved wheels around, still vibrating. Checked wheels for true-ness, no problem found. I feel it in the seat, not in the steering wheel. It's not VCM as it happens under heavy or light throttle. Car is a 2015 AWD and has 99K miles on it. Before I go down the rabbit hole trying to troubleshoot this, any thoughts from anyone? Some things I'm considering as the cause:
- Driveshaft
- half-shafts, front or rear
- Engine mounts
- Transmission mounts
- Some other suspension or driveline components

If anyone had something similar, would be great to hear your story and resolution.