Thanks Duncan,
I thought about changing the battery lead to the other battery but did not think of croc clips (Doh!)
What I meant about checking the bearing is as you say checking its position.
It is a strange one I agree, as it does not always happen.
The radio is an old model, non-DSC, so it might be that the unit is more sensitive than new models to interference. Better electronics and components in modern equipment.
Now to persuade the FPO to spend some more money just after Xmas!
Thanks again
Coddy