Big thank you to IanS16, let me try his white box to see if it cured the problem.
It didn't
So were down to 2 option now, it's either the wiring loom or the converter chip.
My thoughts are, if its the wiring loom, wouldn't the signal drop out, like a speaker cuts out with a loose connection? Mine don't do that, so maybe its just the conversion chip..... i hope