jtroth wrote:Unless the area is wet I would first think about if there are any ductwork routed in those areas. Just the presence of duct work will warm floors and walls in which they are routed under or behind.
Also if a duct work has gaps that also will increase the heat loss behind those areas.
An inspector with thermal imaging may be able to help "see" the concern.
Definitely good insight on to the situation. I wouldn't rush to suspect a leak without looking for other signs. Even a pinhole leak is going to let a lot of water out in a short amount of time. As jtroth stated, get with an inspector that has a thermal camera. I'd also want to put a moisture meter on it. You can pick a cheap one up at a local home improvement store for fairly cheap. While it's not as good as more expensive ones, it'll certainly tell you if there is a high moisture content in the wall should it have soaked through.
I didn't have a picture of an HVAC vent running behind a wall, but I'll add a picture of radiant heat and show how valuable thermal imaging can be as a tool in the arsenal.