Do both have a loud hum when not connected to a computer and running a feed, or is the hum only noticeable when hooked to a computer and a feed is running?
I have found that the best ways to remove any hums are to use mono cables only, don't use stereo patch cables. The other config step is to set your input volume as low as possible, then drive that with the volume from your radio, until you hear clipping. Then go back and adjust your inputs. If you are using a microphone input turn off the mic gain.
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