I can't tell for sure but will fire off a guess... being that I'm from Oregon, the land of crawl spaces.

With all of the new attached housing it's tough to get adequate airflow to crawl spaces. A lot of times since there are units on each side and a garage slab on the other (god forbid your house be wider than your car) the builder is left with only one side to ventilate the crawl.

Due to the lack of cross-flow I see a lot of mechanical fans that 'force' air through the space. A lot of times they are on a humidistat which is tied to a red light in the garage to let you know it's on. I've also seen them tied to the furnace blower fan (the furnace fan doesn't run in the space, the crawl fan is separate and only comes on when the furance fan does).

In any case I'd bet this has something to do with airflow through the crawl space... I could be way off but, again, I'm not sure in the picture that I know what I'm looking at.