We had a similar situation with a guy who's old CRT monitor was "jiggly". I replaced the monitor. Same problem. Replaced the network card. Same problem. Tried r

We had a similar situation with a guy who's old CRT monitor was "jiggly". I replaced the monitor. Same problem. Replaced the network card. Same problem. Tried replacing the whole PC. Same problem. Finally I put his whole set up on a cart with a giant extension cord and wheeled it out into the hallway. The problem went away. Turned out his office had an insufficiently shielded fuse box that was causing magnetic interference.