Can a musty or earthy odor that comes and goes come from somewhere other than basement, crawlspace, wall cavity, attic, closet or supply-air path? The safest answer starts by preserving timing, location and trigger information rather than assigning a cause from one clue.
What this question is really testing
air pressure can move odor from a hidden damp reservoir into a room far from the source. The observation becomes more useful when it can be compared with ground moisture, concealed wet materials, drain pathways, stored contents and outdoor air pulled indoors.
A useful next observation
Compare odor at openings, penetrations and return-air paths. Record the result together with conditions that stayed unchanged so the comparison remains honest.
Safety and handoff boundary
Avoid opening suspect contaminated cavities or using ozone, fogging or unverified chemical treatments. Strong sewage, fuel, solvent or electrical odors require the appropriate professional response. Share a trigger log, airflow conditions, rooms affected, nearby drains or cavities and any moisture readings with their locations.
