It could be noise on the power supply. Perhaps it's some 60 cycle hum on an upper harmonic? Do you have an uninterruptible power supply you can run it on?
It's all in engine, I'm just not sure if it's real time. The less compressed 60 FPS version looks even better. http://www.naughtydog.com/site/post/uncharted_4_a_thiefs_end_2014_e3_trailer/
Really well done. I would get rid of the woman's silhouette to show the scale though. If this thing is supposed to be 60+ feet those are some huuuuuge screws.