I was seeing the exact same thing on my system this summer. I have narrowed it down to a possible heat issue or power (having too many things on the same 15 amp circuit). Since I have not had the dropouts for a few months and it has been much cooler, I am leaning towards the heat problem theory. I was going crazy swapping cables etc., before. Just wanted to let you know that you are not the only person with this problem.

Allen