2009 genesis 4.6 sedan has developed a steering wheel vibration while in gear and at idle. Hyundai service cannot determine why, and now claims that it is not that bad. I disagree, and it was not present in the first 22 months I drove the car. The idle is at about 620 rpm;when it is raised to about 720, the vibration is less severe, but service tells me that the idle cannot be adjusted. Any suggestions?

