#Texel DM-3024
This is called life in the cheap audio lane. All of the inexpensive audio
boards (that tranlates to under $300) can have this problem. In some
computers, there's nothing you can do; no matter what slot you use, no
matter what boards you leave in or take out, the problem persists. In
other computers, you can reduce or eliminate the problem by rearranging the
hardware inside of it.
The problems comes from inadequate shielding of key componenets — they are
picking up noise, or interacting with other components, or acting as an
antenna, etc., etc. The ultimate answer is simply to spend more money for
a higher quality board, such as the Multisound from Turtle Beach, which is
very well shielded from this sort of thing.
Ron