DAB Radio Interference

Has anyone come across this, we live in a rubbish area for AM/Medium Wave and like to listen to Radio 5 Live for the Sport, so we bought a couple of Rechargable  Roberts DAB Radios  

We also have bought a Mains Radio Bedside DAB radio/alarm. The problem is this and has happened this week. In the mornings the reception on the bedside unit is breaking up, when you switch the Battery radio on we get a perfect signal, at night the signal on the bedside unit is perfect as is the portable I even sent for a new aerial from Roberts that has made no difference

Any ideas ?.