Ben Pope wrote:

If I digitise my inputs and select anything other than SPDIF (which is
already digital), the noise floor increases considerably. Probably
30dB+.

You only need to digitise the input if you want to apply effects to
it, such as Reverb or whatever (and lets face it, unless you're doing
Karaoke why would you want to mess about with your inputs... and if
you ARE doing Karaoke, the noise floor is probably the least of your
"noise" problems :-p)

I just tried it when I had the problem, and the problem went away. Didn't
even know what "digitize input " was.

http://www.nforcershq.com/forum/viewtopic.php?t=48238

Others have also had success. It works when there comes a high pitched whine
after the audio has been idle for 20-30 seconds. If one plays sound all the
time, the whine is not heard.
Almost drove me crazy.