I too, have a Nordic XL. I agree there is a dull humming noise when the recirculation pump or heater comes on, but I guess you get used to it. I can hear it kick on but then, I don't even hear the pump.
Have you tried to adjust the two large jets (the two that create the whirlpool effect)?
I place the two of them in a "middle-neutral" position so that minimal water comes out of any of the side jets, and about an equal amount of water comes out both the big jets. It makes it quiet enough that I can hear the bears or skunks sneak up on me!!
Try that, see if it works. I'd be curious if you can resolve the noise problem.
Good luck...