First off, I'm not 100% sure what I have would be considered a french drain. It was there when we purchased the house about a year and a half ago, so I'm not 100% sure on the details. There are two round grates in the two back corners of the yard, each about 8". There is also one in one of the front corners of my yard, right by the curb. It seems like water from the backyard drains down towards this grate in the front yard. In the other front corner of the yard is a storm drain, so maybe the water from the other grate in the back drains into this? Finally, the downspouts in the back and sides of the house drain underground somewhere, I'm assuming into this drainage system.

I've never noticed a drainage problem in the yard, but the other day I found a little bit of water in the HVAC duct at the back of the house. Our house in on a slab, and this appears to be a common problem with the vents that run under the house. I'm already in the process of getting this fixed, however from what I can tell the fact that it's happening means there a drainage issue somewhere. I've never had standing water up against the house, so I assume there's some sort of issue with the drainage system we have. My question is this... How would I go about having this inspected and/or serviced? Would I need to call a plumber, a place like Roto-Rooter, or something entirely different?