My neighbours used to have a hot tub that had a similar hum. We could hear it while we were lying in bed and it was on the other side of the house so the noise must have been bouncing around a bit. It was sat on decking which probably amplified the noise a bit but it's surprising how such a low noise can travel, and how annoying it can be. It should be easy enough to sound-proof the pump housing as long as the pump is sat on something solid. They need to make sure it's sat on rubber and none of the pipework is vibrating against anything.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
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