So I am rendering a scene lit by a HDRI map and rendered on a farm. When I get the shots back there is a subtle flickering along with a bright flash every now and then. I think this may be somehow related to my environment light or sampling, but really have no clue. Any ideas?

Improve the mantra, sampling, give it a try.
Or add some blur in the image.

i assume that some of the machines were not able to load the environment texture.