I had the same type thing happening to me. It was because I had like 5 flourescent lights in the room. If you have flourescent lights turn em off. Or like the other guy said its probably a grounding issue.
Every where that ive tried it there seems to be a bit of buzz. So i doubt its that. However. the previous owner was dutch. Obviously he used a different plug i just used a british wired plug and presumed that would be enough?

Im going to try a couple more places and a different cab befor i start to worry.

any other ideas?