What could cause a "smelly sock" smell seeping into our living room from the crawlspace?
Access the crawlspace and inspect it with a bright light. Assess for damp areas indicative of water penetration from exterior or from leaky pipe(s). Moisture = mildew/mold which can smell. Use coveralls and a dust mask. Look for any dead critters that could be causing this.

Certain plants and trees drop leaves and stuff that smell (eucalyptus, for example) if left sitting to get damp, ensure accumulated plant matter and debris are raked away from your home.

Whatever issue is found, fix it. Damp nasty soil can often be treated with hydrated lime powder to remove and prevent future odors.