Two things to check:
1) Make sure that the XLR outputs are connected properly – ALL pins must be connected, otherwise you will get all sorts of strange noises.
2) You may just have too much gain on the signal so that you are listening to the noise floor of the Orville – make sure that the Orville's peak level (all meters lit) does not overdrive your speakers.
The Orville has a signal to noise ratio of around 110dB – this means that if you follow the output with 100dB of gain (plugging it into a mike input for example) it will sound dreadful (much as you describe). But, it will also be unuseable, as a full level signal will be totally clipped.