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When you stand on an underground belt entrance and bump in to certain objects, that causes the screen to vibrate and appear fuzzy. Especially noticable with fast/express underground belts and zoomed in.
The situation where this comes up most is when you have chests on the same row as your belts and use underground belts to pass them. (and you stroll around your base checking things out and inavoidably get transported by standing still on belts)
On the screenshot, objects to the left cause this vibrating, objects to the right do not. Tested in 0.9.8 and 0.10.12.