According to my sources there are three transmitters serving DAB to Aberdeen they are Durris (NO763899), Meldrum (NJ761329) and Mormond Hill (NJ983569). It surprises me that you can get the commercial services and not the BBC ones, in my experience it's usually the other way round. Are you using the built in aerial? I'd recommend getting an external jobbie if your signal strength is iffy. Whats your AGC on the existing services.