My 2008 Ranger XLT started vibrating on Highway driving three months ago. My mechanic changed all 4 shocked and ball joints, rotated and balanced tires, no luck. I have Goodyear tires plenty of thread, but I swear one looks like it has a sidewall bubble/blemish. The front end does not shimmy or vibrate, this humming and vibration you can feel in the seat as you drive. My mechanic thinks it can be anything from bad tires, to warped driveshaft, unjoints or rear end issues. I am wondering wheel bearings. If I go process of elimination it will cost a small fortune. Therefore that’s why I am reaching out here, any ideas?