I have a 2009 Nissan Altima that had 114k miles when it got the same annoying vibration problem at 1200-1500 rpm. In addition to the vibrations, I would also hear ticking noises upon cold engine start-up, the engine would make a light grinding noise when idling in gear, and the car would lurch in at low rpms. Based on this post, I took it in to the dealer and asked them to replace the alternator. They were skeptical that a failing alternator bearing would cause all of these symptoms, especially when the alternator was putting out full voltage, but when they replaced it, the problems were completely gone. The car doesn't grind when idling in gear, it doesn't vibrate at 1200-1500 rpm, and my Altima doesn't lurch in low gear anymore. I couldn't be happier!
Yes, my vibration is 100% better.
I thought it was the new CVT causing the problem!
It was the alternator.
My dealer showed me the TSB and replaced the alternator. Skeptical, I drove it off the lot and to my surprise, it is fixed and smooth once again.