horizontal lines on external display

I have just received a refurbished mac mini (previous generation) purchased from Apple. When attached to my monitor, an LG Flatron L204WT, it displays thin horizontal lines which run the width of the display. They are present across the entire display. The lines are most noticeable on a solid grey colour. They are not visible in a gradient, such as the drop shadows around windows. They look similar to horizontal scan lines on a CRT television.

I use the same monitor as an external display for my macbook; it doesn't have this problem.

Has anyone else had this issue? I realize I can take it to Apple for repair, but I would hate to find out this is a chronic problem. Coupled with the annoying chirping noise the mini is making, this is a bit of a let down... I'm considering returning it. Anyone had wither of these issues with the redesigned mac mini?

Thanks!