They were carrying something to the chopper' Interdasting that they had white protective gear on.
this shows several choppers flying.
MILITARY EXERCISE: The U.S. Army is conducting military training in the greater Los Angeles and Long Beach areas tonight until Feb. 9. Downtown LA residents are reporting seeing helicopters and hearing explosions. @MizSkellington
https://twitter.com/CBSLA/status/1092659229268340736?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1092659229268340736&ref_url=https%3A%2F%2Fwww.haaretz.com%2Fworld-news%2Floud-booms-shake-los-angeles-as-u-s-army-conducts-training-exercise-1.6912136