Ground Looping Troubles

[Antee]

This is my problem: i'm moving from pc to imac... now my set up is the imac, an m-audio (firewire audiophile) soundcard connected to the imac, the 404 connected to the m-audio input line and the m-audio output are connected with my monitor speakers Samson Resolv 50a.
With my old pc, i used the same connection and i never had trouble, but now with the imac i hear some strange freq on the speakers, something around 50hz and sometimes some metallic sounds... also when i turn of my speaker i hear a bad sound... now i've disconnect the speakers... on the web i've found some shit about ground looping, some cats suggest to isolate with some isulating tape the tabs on the shuko outlet, i've tried this shit but it doesn't work for me... other cats suggest to truncate the central picket of the power plug... but i don't want more trubles.
I'm deperate sp-heads, any advices?
Sorry for my bad english, peace from Italy.
Antee

[IIIII]

try a different outlet that's nearby. i get a buzz from some plugs and not from others... good luck. a surge protector helps sometimes too, but i don't know much about this stuff