Grey banding on monitor

My Smile 17" CRT monitor has developed a fault where horizontal grey bands are overlaid on the display. The effect is rather like viewing the screen through a filter. The problem occurs when text is displayed and is related to the darkness of the text. White text causes no banding, while bold black text is particularly bad. In short, the darker the text, the darker the banding. The bands are always transparent and the display can be seen underneath.

I`d be grateful if anyone could suggest the possible cause. I have already checked all the cabling and the Windows display settings with no positive result.

TIA,
Dogsbody.

I swapped out monitors. no luck.
I reset the origional bios.
I reinstalled windows98. no luck.
I still have these gray bands on my screen.
So what is left? The Graphics card?
The Mother board?
Any thoughts?

Thanks,
Phil

no
I am not using a switch box or extension cable.
The monitor cable goes from the monitor to the video card.

Thanks for responding,
Phil