I have a simple and I think common question:

How does one eliminate the annoying feedback heard from a stereo's speakers
when a computer's sound card audio output is plugged into the stereo´s aux
input?
Also, there is the same but louder feedback when the antenna cable from the
wall is plugged into the VCR (which is connected to another of the stereo´s
aux inputs).
The phonograph, cd player, and audio deck do not cause any feedback so I
leave them plugged in. By the way, when I mean feedback, i´m refering to
the loud humming/buzzing thru the speakers. The stereo pre-amp is a Marantz
from the mid-1970s and thus does not have any of the fancy "video" inputs.

If this question has already been asked, please excuse me. I could not find
it logged. Thanks for any help!

-Tom