All good advice so far, especially the appliance moving and the drain traps. Do that.
From my halcyon days as a landlord, smells tended to be temporary: something died, crapped, hurled, etc. and those things have a olfactory lifespan, an arc of pungency, even the serious, cat spray, dead rat in the wall stuff.
If you have central air and heating, inspect all that stuff...ducts carry it all.
A trick I used a few times, passed down through generations of landlords, is to seal each room as best you can (I have taped over - using cheap plastic painters cloth - entrances without doors) and try and isolate the smell that way.
Good luck. Mold was my biggest problem....look for that while you are at it
