My brother is having this issue with his car. After about 20 minutes of driving at highway speeds, the car starts vibrating when the gas is on, but goes away when the gas if off. He took it to the local mechanic but they won't drive it long enough to have it happen. No reason in particular, but he thinks it might be the transmission.
It's a 2014 Ford Escape Titanium with 95K miles on it. He just had all the wheels balanced and the tires are new.
Video of it happening: http://thegiant.org/IMG_5577.mov
Any ideas where to begin?