Static or something else?

Bit of a strange one this....

I have a Cambridge Audio set-up (amp, DAB, CD) with a matching iPod dock on top. I don't use it daily so it's left alone for periods of time, however when I do switch on the iPod there's a very evident electrical 'buzz' that whilst isn't sufficient to give an actual shock, there's definitely a tiny tingle.

This obviously isn't right and I wonder if anyone has any ideas as to the cause? I've checked every connection, both audio and electrical but everything appears ok.

Thanks.