I have a 2015 Subaru Legacy with about 26000 miles. At around 70mph I get a slight vibration. Sometimes it's more noticeable than other times. I've had it to the Subaru dealer twice and the tech can't feel it. Both times they balanced the tires and send me on my way. It's still there. To me it feels kind of like an out of balance drive shaft or a bad U joint. The motor is smooth as glass. Any ideas where I should look or has anyone else had this problem. I was very smooth until I had about 18000 miles on it.