Humming noises generally occur when monitoring an input signal that suffers from a low signal to noise (S/N) ratio. In other words, a signal that is not that much louder than the noise that is also present on the same channel. This noise is greatly accentuated when lots of gain is applied to the instrument (MIC/INST) Input. To resolve this please follow the instructions below:
1. Make sure that MIC/INST1 and MIC/INST2 gain is not set to max position (+54db gain increase) Initially. Start with yur input gain low. Try to boost the signal from the device being recorded first. Ex: Turn up your guitar or keyboard's output volume before trying to boost MIC/INST signal. Also, keep in mind that the INST input is a high-Z input; therefore a maximum gain setting applied to an incoming signal with a low S/N ratio will most likely produce a very loud and noisy signal in your Monitor mixer.
2. Begin your recording process with the cleanest input signal possible. Make sure that all of your equipment is properly grounded. Use premium sheilded cables to connect your musical instruments to your audio interface. Always use balanced TRS cables for instruments with 1/4" outputs. Power conditioners and line filters can also help clean up hums and buzzes throughout your entire recording set-up.
3. Open your device's control panel software. Click the monitor mixer tab at the bottom in order to open the Monitor mixer dialogue. Adjust levels as needed. Try to strike a balance. In some cases, It may be necessary to turn off monitoring from input1/2(I2S 0/1) to output1/2.