Electric "buzzing" from speakers

I have an issue with my old creative speakers. When i have them turn on and hold front pannel cabble in my hands its starts buzzing in speakers, but when i touch my case(lancool k58) with it it makes ieven lauder buzzing(even if my pc is disconnected from power). In my all system i even heard big, shurt "buzz" during boot up for years, new rig doesnt have that but still.

Is it safe for my pc? Is there something wrong with speakers or something(those are subwoofer and pilot speakers)?

I'd imagine it's a ground loop issue or a shielding issue with the front panel audio cables. I haven't done much in rectifying these type of issues with pcs, but im sure someone will be along who has.

Edit: just re-read your first sentence. Is it only when youre holding the cable? Is it the internal front panel audio that goes to the motherboard or an external one?