[Arran]

That buzz is external to the radio, either it is RF interference or it's coming down the power line. I had a problem like that with some radios in my late Uncle's trailer, it was not a buzz as such but a sort of rhythmic noise almost like it was modulated, but for the past year I haven't heard it, in fact I haven't heard it since they replaced the nearby power pole. That noise coming out of the hippo sounds like a fluorescent light or a dimmer switch, though it could also be a defective transformer on the power pole.
Regards
Arran