As mentioned, if you are wiring the three pins to a single XLR that goes into a balanced input, and you are outputting the same signal to both audio channels, you are going to get a lot of noise and very little signal (because the two signals are cancelling each other out).
If you have Bela cape, there are balanced, DC-coupled output pins available as unsoldered pads on the board (search for the label J9, just behind the analog inputs).
Also, What configuration are you testing this on? The noise you have may well be some sort of ground loop.