The hum issue is one that has been improving over time but proven quite difficult to resolve completely.
The transformer supports both the DMM and DAQ model. As such, there are 2 transformers that are present in the instrument, 1 for the DMM and 1 for the DAQ that powers the switch modules.
In order to fit both of these transformers into the instrument (for both models), they required being bolted together in a metal frame that is affixed to the chassis.
The transformer design and housing is the way it is completely for cost and mechanical reasons. However, this has actually made the hum problem worse.
It turns out that this metal bracket actually vibrates and sort of resonates the sound not only from the natural transformer vibration but introduces larger harmonics of it.
The transformers are *double* dipped in varnish AND the metal bracket has an epoxy fillet along the perimeter of the mounting to help dampen vibrations. Yet still, some hum can be heard in some cases.
The factory has some controls in place to make sure it is not "too bad" -- again though, this is subjective!