It's probably shuddering caused by friction of the nylon sliders running on the mechanism's tracks or runners.
My 2011 did the same thing at about the same mileage, until I pulled the tupperware off the nose, cleaned the old grease out, polished the runners with 2000 grit & metal polish, and re-lubed with some moly-based grease.
I plan to re-lube the runners again once the season is over.
Another thing is to check the cable tension while you have the nose tupperware off. I think the cable stretches a little over time, and the resulting slack exaggerates the shuddering.
You'll have to loosen the cable pulley wheel shown in the image. IIRC, there's a hex key bolt hidden behind part of the mechanism in this photo. Raise the mechanism with the power on while making the adjustment.
Then loosen the locknut, and turn the adjuster bolt a little to take up a bit of slack. Don't tighten it too much, but it should be snug.
Re-tighten the locknut, then the pulley bolt.