Rear-end Noise After 4-link

[camarosaurusrex]

I am at a loss and not to much knowledge. I had ridetech's 4link installed by a respected builder and now have a strange "chatter" "shudder" don't really know how to describe it(video attached). The sound shows up around 30mph and will disappear if I go higher. The builder is out of town for a bit so i can't go back to him yet and thought I would ask around. The sound comes in pretty early in the video and you can hear it though out if you can stand to watch it.
Any help or ideas to bring back to the builder would be great Thank you
https://youtu.be/SUIWBC4AY8g