What causes this monitor problem?

I keep seeing some horizontal refresh or sync lines when playing videos, either through youtube or other players. They mostly appear when changing scenes or fast action. I hope you know what I mean, but I am thinking its my cheap Dell 24" monitor. It can't be my card cause my old ATI 5670 did it too.

dja2k

I am also looking into buying a new monitor. I wanted an LED for less strain on eyes and also Height, Pivot, Swivel, Tilt. I don't know if going IPS is a good move, since I do daily use, play lots of video files, and some gaming.

UPDATE:
Anyone have any comments on the Asus PA246Q 24.1 IPS monitor?

dja2k