My 2003 V-70 has developed a vibration this past week, at least that what my daughter told me when she drove home from college today. The shake manifests itself on the highway between 60-70 mph. When I test drove it this evening, I found that I could make the vibration come and go by accelerating and decelerating. I don't feel vibration through the steering wheel, but rather through my seat. I put the up on a hoist at work and checked for an out of round tire/shifted belt. I also checked tire pressure, wheel play and strut condition. The tires are fairly new and recently balanced and everything else checks out favorably. Motor mount(s) perhaps? Does this make sense? Is there a preferred manner of testing them?