well here's my thoughts.
sounds like the Automatic Level Control is bringing up the level of noise that is being introduced at the input.
the unit has a mic and a line input. coming from an X32, it should be plugged into the line input. the mic input has voltage on it for an electret mic and would probably cause this issue if it's being used.
if the line input is being used, the input level control may be too high.
or, the adapter you are using to get the XLR to the 1/4" input may be wrong. it should be a proper XLR to T-S unbalanced adapter, or perhaps a balanced to unbalanced transformer.
in short, assuming the unit isn't just broken, something is causing the noise at teh input and then the ALC is raising that level in the absence of input signal to the loud level you're hearing. figure out what is causing the noise at the input, and you'll find the problem.
i think.