Greetings,
This might be a complete red herring but is your tv one of these that doesn`t like a mixture of inputs connected at the same time? Like for example the rear normal inputs and a front (or side) AV input together causing signal degradation? I managed to get something similar once on my Sony tv cos it wasn`t too happy with both the input from my camera coming in at the AV on the front whilst I had a signal coming in on the scart connection at the back... (forgot to switch of the VCR that was connected!).