mysterious dirt odor

I’ve lived in my house for several years without any smell issues. For the past few days, when I go outside for more than 5 minutes, when I go back into my house it’s apparent that there’s a very distinct "dirt smell" permeating the entire house and basement. It’s not subtle. My nose gets completely used to it in about 30 seconds, so I have very short stints of sniffing around trying to find the source.

I’ve looked everywhere for water spots or dampness, and I couldn’t find anything.

Any suggestions on things to look for, or what kind of service could help out?