What could be causing an odor of mulch inside my house? I have not used any mulch around the outside of my home. This odor started a couple of weeks ago, just in one section of my house but we could never figure out what it was or where it was coming from. It would come and go, but now the odor seems to have reappeared in more areas of the house. Any ideas?

Odors that come and go are tough to diagnos on the inetrnet. Mulch smells like mold and mildew to be so maybe that's what you have is mold somewhere. Sewer drain lines also smell from sewer gas and/or biofilm that builds up inside the pipes. Your vent stack goes out the top of the home via the roof and vemts this air. Sometimes, deoending on weather coditions, that stale air falls back down the outer walls and can sneak back inside the home. Have you had and drain problems at all lately?