Telephone Mode On Radio?!

I have been getting an issue recently that the radio/CD/Tape player will switch off and 'Telephone' will be displayed on the radio front panel......This seems to happen when the area around the radio gets hot due to the heater being on on long journeys.

If I pull at the front of the radio housing it switched back temporarily to radio, but will then happen again, it would appear to be a short connection due to heat or a loose connection somewhere.... has anybody else experienced this?

Thanks

Chris