Another source (speculation at this time) of your troubles.
The WSP uses a cheap switching PSU. When these aren't driven to high loads, the switching circuits slow down the switching rates of the outputs to conserve power. When the power level out is high, the circuit switches faster to counteract.
If the supply load is small (as it would appear from some of the comment above), then there is sometimes a source of 'beat' frequencies between the Video cicuitry and the switching PSU noise on the supply lines.
I've noticed that there are a number of positions on the WSP PCB for additional filtering circuitry parts which aren't actually fitted with anything. Don't forget that the WSP is designed to a price (not a function) and small items like $0.20c filtering parts aren't fitted if the circuit runs fine for most machines.
It could be that the PSU is just generating noise that's getting through the (cheap?) filtering on the board.
Compare the price of a $200 Matrox WIZZ2K (or whatever) video card with a $50 WSP and you see the point?
That's not to say that the WSP shouldn't work on a TV - it's meant too after all.