Bolero volume problem?

On a few occasions recently I have been sitting in the car, without the engine running, listening to the radio and just enjoying my new Yeti. If I then start the car the volume goes very low and has to be turned up high. Turning the radio off and on again doesn't resolve the problem but the next time I restart the engine I am deafened!

I have set the start up volume using the setup and it seems to stay at the stored level.

I must admit that the manual(and the car handbook) is one of the worst I have ever come across so I might be misreading something.

It also happens if I stall the engine when the radio is on. When I restart the engine the volume is again down to a very low level.

I have got into the habit of turning the radio OFF before killing the engine but I'm sure it shouldn't happen. Anyone got any ideas?

Fred