I moved away from the amp and nothing changed.
I also tried the same setup, but using my Trace combo. Same bass, same bass cable, same XLR, and no buzzing at all from the monitor.
The Trace has no Pre/Post/Line/Mic options, just the XLR socket. I dont know what the D.I. is set to inside the amp, but the Trace master volume still works, and
so does the 12 band graphic, so assume its Post EQ
On the Genz, the master volume is taken out of the equation in Post EQ option.