I have the same thing....but different ! I recently installed the Throttlemeister heavies on my 2011. Up to speed everything is fine but at idle, and just off idle, the left bar vibrates so much you can hear it. If I take my hand off the left grip it is even louder. I was just about to check it again to make sure it is tight. This is weird . All the fuss about C14 riders with numb right hands and I have a numb left one.
I don't hear any vibration from the left but i can definitely feel more in the left at any speed and at the 3500 rpm on hwy is when it gets significantly buzzier and settles down at 4k, but i dont want to sustain that high of a speed. So what i did was put the stock bar end on and figure of course the rubber insert helps, but i noticed that there was more of a gap from bar end to grip end with the stock and i had no shims in throttlemeister left side. So i figured maybe the weight is out further with the stock and the weight being in closer created a bad harmonic response at hwy speeds, so i shimmed the throttle meister on the lefts side out to match the gap of the stock. Who knows.... It might not do anything. I havent ridden it yet that way since im on vacation. Im completely happy with the throttle side being vibration free at any rpm.... Ridiculously smooth actually, so prob why the slight vibration of the left is exagerated for me.