Locating the Source of a Bad Smell?

I live in a garage apt (two car garage apt above it) and before I moved in my landlord gutted it and refurbished the whole place. I started to notice a nasty smell in my kid's room that I thought was just my kid stinking of body odor. It smelled exactly like BO then would go away for a week or two, then I would smell it again only stronger.

Just last week my dog tried ripping apart the door to the room from the bottom, desparately trying to dig her way into the room. When I caught her doing this I opened the door and she bolted under the bed and started frantically sniffing the rug and digging into it as well. I removed her from the room barricading her to keep her from tearing more of it off. But she stands in front of the door barking and crying and has been agitated by whatever is in there. Sometimes she'll run and hide for hours at a time in places she normally won't go and she's never behaved this way before.

I cleaned the room several times thoroughly top to bottom failing to locate the source of the smell. What the heck is it? It has to be a dead rodent in the walls, but how would I find it and why is my dog reacting to it like it's harmful?

By Angib