Noisy bathroom fan's motor

Help! We are now 2+ years in a tri-level house that was buiilt in the late 70s and added on to several times. The most recent issue discovered is that ductwork, evidently built into the slab for one section of our home, once fed by a downdraft furnace in the garage, is flooded. One of the many previous owners evidently discovered this, abandoned the ductwork, replaced the furnace and reworked the air paths using flexible ductork through the attic. My issue is that we have a hole in the garage floor.. and a ductwork fingersystem under 1/3 of our house, that is full of water. We live on a very high-water tabel and I do not believe drainage is the issue.. or anything I can successfully address. We would evenutally like to convert this garage into a finished room.. and would like to mitigate the risk of a potential mold-farm under our house. Can anybody tell me how this can be filled in? Or if there are other issues that I am unaware of? Thank you!

I have a mother-in-law apartment below our house that currently houses my wife's niece. She is a smoker and a heavy perfume wearer, and these odors passively migrate from her living area to ours through the ductwork when the heating system is not actively moving air (to my annoyance:mad: ). I checked the heater room and it's free of odors and I notice very little odor when the heat is on. This appears to be coming back from the heater vent in her bath and living area through to my heater vents upstairs. I thought of trying to find an in-line louver, but I don't see where this type of system exists. In another forum someone suggested a charcoal filter. Is this a viable idea and if so, would I place them at all of my exhaust locations? Thanks in advance.