I've searched a bit and it seems most "damp garage floor" problems come down to condensation. Mine is different. In addition to a desire to understand the problem and identify a solution, I at minimum would like to know what kind of tradesperson to call in for this type of issue. Damp basement people? Concrete guy?

My garage has a door to the laundry room at one end, with two steps leading up to the door. Pretty standard. I'm getting two circles of moisture, about 2' in diameter, one on each side of the stairs (and therefore almost against the back wall of the garage.) The center of the circle seems wettest. I think there is some efflorescence in the damp patches. It never gets so wet that there is loose water visible.

There are no downspouts anywhere near that particular spot. There is crawlspace underneath the laundry room, which generally stays dry. Appearance of moisture doesn't seem particularly well correlated to weather; e.g., it doesn't get any wetter after heavy rain.

I'm stumped. Who would I bring in to look at this?