Hello Hodgey,
Interesting that you suggested the s-video cable. It is a brand new cable (5m) however I have since found this link that suggests that a poorly shielded S-Video cable can be subject to external RF and the example they give is very similar to the original issue (
http://www.avartifactatlas.com/artif..._decoding.html ). I have ordered a better quality cable (as much as you can tell by ordering online) and will route it away from all other cables and machines to see if it makes a difference.
Will also try component output and take a look at the power supply as well.
I appreciate your time to reply Hodgey.
I'll let you know what I find.
dc