Some answers here may be useful:
http://www.radioandtvhelp.co.uk/interference/rtis_radio/lost_DABradio
I have two DAB radios, one portable Roberts and a dedicated PURE tuner connected to an external aerial on the roof. This latter has never been a problem, but the Roberts does occasionally have this burbling noise, sometimes when I am physically near it. The aerials on all portable radios are inside the house (usually) and it seems to me that most times they're working just on the edge of their ability to receive a good signal. Yes, in my opinion the DAB conversion has been a fiasco and it's even more galling to know that DAB+ is not compatible with DAB. Frankly, IMHO, we've been duped and someone (or more) should really be in prison.