Nobody can tell you anything without exact render settings and info on what you use to actually review your work. You're just throwing around a lot of (unfounded) assumptions. This could merely be a playback issue due to the USB drive's low data rate and then what?
So here's the deal, when looked at frame by frame the "static" is in exactly the same place/frame number every time even when not played back from the usb drive.
So not a playback issue.
When no settings change between renders and the only variable is the connection to the drive (internal vs. external), to most logical and sentient beings that defines the source of the problem.
Seriously a "low data rate" from a USB 3.0?
This has been a problem for more than one generation of AE.
Lastly there are no "unfounded" or otherwise "assumptions" in my original message, there are two examples of my experience and the conclusions I made from those experiences.
Have yourself a fun little day.
One more thing, as in any good scientific experiment, the proof of concept lies in the ability to repeat the experiment with the same results.
While the position/frame reference of the static/interference is variable the overall result, no static/interference vs. plenty of static/interference does repeat every time.
Again have yourself a fun little day.