Buzzing when interior lights go on / off

[Rololux]

This is a strange one - when I unlock the van, there is a low level buzzing sound that comes from somewhere under the bonnet area. If I close the door, the interior lights stay on for 30 secs or so, and when they go off (fade down) the buzzing sounds happens again - at the point when the lights are fully off. I've had the van for over a year, and have never noticed this before - maybe it was always there, but maybe it is new.

Any ideas? Anyone else got this?

Thanks

 

[flying banana]

When you open the drivers door all sorts of computers spin into life. Including the fuel priming pump. Even though its not a computer. Maybe it's that?