Sounds like a power leak/interference problem. Isolate your cable (i.e. hold it up in the air and make sure it doesn't touch any other cables, power or otherwise). If that helps, then it's interference from power cords/etc. and you'll have to reroute accordingly. (Issues like that can crop up even though to your eye nothing has changed about the set-up to warrant it.)
If not, you'll have to describe the issue a bit more clearly than "little dots" LOL.