Vibration at 42 MPH on a pull

[JH51]

HI!
I purchased a new 2007 Versa hatchback 1.8 with the CVT tansmission in 2006 for my wife. It has 63K on it now. Other than regular maintenance we haven't had much trouble out of it. About two months ago she had new tires put on it along with new Nissan rotors and pads. The tires were the exact same size and manufacturer as came on the car new. Shortly after the repairs I drove it and noticed that it had a vibration at about 42 MPH on a pull. I told her that she needed to take it back to the dealership, where she works by the way, and have them recheck the balance of the tires and if that didn't fix the problem then have them rotate the tires to see if we had got a bad tire. Neither one of those things fixed the problem. So she took it to the Nissan dealership, which her boss also owns. They checked it out and agreed that it had a problem, but said they didn't know what exactly was causing it. They ruled out wheel bearings and said that maybe a CV joint is drying up. Since the vibration is so slight right now they told her to run it and if that is the problem it will get worse. What do you think could be causing this? I'm thinking maybe the transmission? Should I go ahead and trade this car?
Thanks for any help!
JH51

[MaximA32]

I think that trading it in would be a bit of an over reaction at this time but I would definitely see if you can press the dealer to be a little more specific. How severe is the vibration? You only notice it at 42 mph specifically? That seems odd.