How to get rid of hum from soundcard

Help,

I am to new to this group to have an intelligent slink question so I'll start with a simple analog question ...

I am trying to connect my PC's Sound Card line out to my Sony reciever's line in (tape).

I have tried four different computers all but an IBM Intelistation use either SB Live, Live Value or AWE 64. Hooking up to my notebook solves the problem but it isn't an option.

No matter how well I ground the chassis of the reciever (grounding post) to the chassis ground (or card ground) I can't get rid of the hum. The computers are on a seperate circuit then the reciever ... but I have tried then on the same grounded circuit with the same result.

I have made several cables from a single ground wire to shielded microphone caable and their is no difference.

Does any one know of a schematic for some sort of isolation circuit or product that will solve this problem.

Thanks for your time,