I was installing some software on the receptionist's PC at a client in an office block in the 90's. The screen glitched sideways severely while I was doing it and I mentioned it to her. She said "it does that all the time. They've replaced my screen 3 times and it never goes away."
I sat there finishing off the install taking in the environment and then said - "let's try something". I moved the screen to the other end of her desk and the glitching stopped. She was overjoyed and wanted to know how I fixed it.
I told her the screen was right up against the wall and the glitch happened everytime the elevator went past.
Pretty sad their hardware guys didn't figure it out.