Trbst.Video distortion, interference. Monitor or video card?

Ok, i'm in a situation here. My monitor is currently an old 17" CRT, it would probably make sense that its dying by now. My processor/ram have also been with me for a good couple of years.
My videocard/motherboard however are both new (well, a month old) an OEM 7900gs and a nf4x motherboard.

In the last few days i've began to notice a weird kind of video distortion. It's especially noticeable with text, with the font having seeming like there is interference with it like the image is being bled but only in the form of flashing hair thin horizontal, lines. It is occasionally noticeable in images aswell, and one became so bad that a game became unplayable(only a single occourance though).

I thought i'd attributed it to my 1.55 cpu voltage, and turning it down seemed to have an affect as there were no lines on the POST screen as there usually were, but now im equally enclined to believe it has something todo with the monitor self calibration as it turns on.

These lines are far bigger and more noticeable at lower resolutions, infact im not even sure if they even occur nearly as often at the monitors standard resolution (1024x780), and its entirely inconsistent aswell, sometimes it will become really bad, then ill fiddle with the resolution/turn the monitor off/on a few times and maybe restart and itll go.

Ive tried moving the monitor(away from possible magnetic interference)/checking cables/cleaning my graph card/cleaning my processor and now im stumped.

If this is purely a monitor error thats fine, I was planning on buying a new one soon anyway. But if its a video/processor problem thats a much bigger deal. I'm quite isolated so theres no quick/inexpensive way for me to check if its my monitor or vid card by simply hooking it up to another machine, can anyone think of any other way for me to determine and possibly even solve the problem??

nate