I have a Belkin KVM (not DVI though) and used to get terrible flicker on my LCD monitor, lots of horizontal lines and interference - it was almost unusable at times. I finally worked out that I had to change the refresh rate. I can't remember the refresh rates involved, but the display is rock solid now. It might be worth experimenting with different refresh rates if you haven't ruled that out already.
But as I say, I don't have DVI or know much about it, so maybe refresh rates are irrelevant.
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Geoff
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Mk1 Blue - was 4GB, now 16GB
Mk2 Red - was 12GB, now 60GB