How can I fix my Ferguson FRG-R121D DAB Radio?

This Radio worked well in dab and fm for a long time, then a humming / buzzing noise developed on dab. Initially the fm reception was Ok then the buzzing noise began there too. Now as soon as it is turned on the noise is present and quite loud. It sounds like a blown speaker. I've seen the same problem described elsewhwere on the net but no answers or repair suggestions.