Hi gaunty, long time no see.
I read about a problem like this once that was finally traced to a short antennae lead. As the temperature reduced (at altitude), the metal contracted, disconnecting the internal wire from the socket, while the insulation remained connected. Once the aircraft decended the metal expanded again, and pushed itself back into the socket. Consequence of someone who couldn't be bothered cutting a longer lead, instead of just slightly stretching the one they had to fit the connection.