I've got just over 4,100 miles on my ST2 now, and I've never had any vibration at ANY speed. It's one of the smoothest cars I've ever owned. Something is definitely not right. I really don't have any idea what could be causing it, so I'm sorry that I'm no help there, but if they can't figure it out...take it to a different dealer!
2012 Ford Focus Titanium hatch, traded for...
2013 Ford Focus ST...and LOVE IT!!!