[DGW]

I drove the car yesterday, and 08 987, and noticed a vibration that I don't think I have ever experienced in a car. I suspect its tires but on the off chance its something more serious I though I would check here.
It became most noticeable around 60 mph up through 70 which is as fast as I went. It would start in my feet and come up through the seat. Then it went away and started over and continued to cycle like this.

Its not the road, I've driven other cars on the same road without anything like this. We took a 3000+ road trip about 3 weeks ago and this vibration did not occur. I had new rear tires mounted on the car before the trip. The tires are Continentals.