The radio can pick up interference from the Ballast of the lights.
You can correct/minimise this by positioning the aerial away from the Ballast, which is located on the cabin roof. Remember that the aerial will still need to ideally be in an upwards position to maximise radio reception.
Your radio might also buzz if it is unable to correctly tune into a particular station.
Alternatively you may experience buzzing from other items either in your house or if you live close to Hospitals, Overhead pylons etc that emit radio frequencies.