Bizarre "dirty" smell around house
When was the 'hospital grade' filtration system installed? What is the nature of the filter media and the physical arrangement of the filters? Where is the air handler located? in the attic? in a closet in the living space? in the basement?

You might try a less restrictive filter. The more restrictive the filter is, the lower is the pressure in the region between the filter and the blower motor.  If there is a leak in this region, outside unfiltered air will be pulled in from a region of higher pressure, bypassing the filter and perhaps carrying musty odors. If the duct work in this region suddenly sprang a leak, then this would explain the sudden appearance of this off odor. Inspect the duct work carefully in this low pressure area.

There are reports of highly restrictive filters putting such a high load on the blower fan motor that it increased the electric current flow in the motor above the design limit and drastically shortened the service life of the motor. Could this smell be from an overheated motor?