unwelcome critters

Before I go and call up an expensive exterminator, I thought I'd ask yall what you'd do.

My dog, Shadow smells something in one corner of the house. He scratches at the area and whines. Within the last two days, I've started smelling a pee smell there (like cats). Once I heard scratching. I haven't noticed any shavings of wood or anything chewed open or little poops around. Still, I think somethings in there. What would you do???

thanks,
Harper