Humming Sound of UPS vs DSP Inverter
The humming and particularly the growling are indicative of demonic posession.  Have you noticed dead cats outside and that birds don't fly over the house anymore?

OK, back to real science.  Yes these things can hum.  There are high currents sloshing around and magnetic fields coming and going at the power frequency and also at the switching frequency.  Some noise from inductors and other parts is normal.  This mostly comes from the force on the turns of wire resulting from the current and the magnetic field.

If the unit seems to be operating properly within expected efficiency (not getting excessively hot), then I wouldn't worry about it.