Having never used the routing presets, I had to look at "DAW TRACKING" to see what it did. Turns out, all it really does is mute your inputs so that all you hear is the DAW's output. You could achieve the same result more conveniently by switching mixes via the tabs across the top. Just set up "Mix 3" with every channel set to "OFF". Then it's one click to switch between the two settings.
But this also suggests that some or most of your noise had been coming through one of the input channels, rather than from the interface itself as I had assumed. Have you tried muting each channel one at a time to see if the noise goes away when one of them is muted?
My standard setup is to have everything muted, and just enable whatever channel(s) I'm recording. Just as I'd do with a real mixer.