The removal tools finally arrived the other day so i finally got chance to remove the radio. The large quadlock connector looked connected properly but it appears that someone has used a different connector at some point as there was a lot of push connectors.
The single aerial plug looked in good condition and was connected. I decided to do a bit of an experiment to see if the interference was still there with the aerial cable disconnected and it wasn't. Does that indicate that the interference is coming down the aerial cable or was it missing just because there was no signal for it to interfere with?