Please help: Toshiba 27A32 - Scrolling band of distortion?

[Heartburn]

Two nights ago I set up my 27" Toshiba 27A32 using svideo and an GeForce2MX graphics gard.  After some tweaking, everything looked pretty good.  I played around last night, and it looked good, too.  Tonight I notice a weird 'band' which slowly scrolls  from the bottom of the picture to the top, and distorts the image.  When it reaches the top it disappears for a moment then comes back from the bottom again.

The distortion usually appears to be a 'bulge' to the left, and occasionally is quite severe.  I checked to ensure that no major electronics were operating today but not yesterday, which might have caused interference.  Here's a rough indication of what I'm seeing:


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<---------------------------------------<       This is the band which scrolls slowly upward
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Does anyone know what could cause this?  I tried a few different things to remedy the situation:

1. Turning off my air conditioner (who knows, it was worth a try)
2. Changing the refresh rate using MAME's parameters

I'm out of ideas.

Thanks!

[Witchboard]

Is this in a cabinet, or on your desk?  The only thing I could think of would be what you're thinking.  Make sure there aren't any fans close to the monitor and if it's in a cab, try switching off your marquee light.  I'm sure one of the monitor gurus will have some better insight.

[Heartburn]

It's not in the cabinet.  The only electronics within 10' are the PC, a VCR and a DVD player, the last of which were in standby mode.  Plus, they were there the previous nights when the interference was not present.

[Witchboard]

Looks like we'll have to wait for one of the more monitor savvy people to show up then.  I hope you get it figured out.