Hole in baseboard. Termites??

I was cleaning my bathroom yesterday and noticed a section of the baseboard sounded hollow. I poked around and tore right through to see there was no wood. The paint was covering the hole like a piece of thin paper. The hole was maybe 3 inches across. That baseboard was put in, along with new drywall 3.5 years ago (summer 2010). Does this sound like the work of termites? That's the only section that sounded hollow. It's in an area between the toilet and tub/shower...so that area gets more moisture I'd imagine. There are rats living in the attic/behind the walls. I hear them run around at night. They get in/out through a portal in the garage. But I don't think they would've cause the hole in the baseboard. But there's no hole like this anywhere I've seen. If it is termites, is spot spraying an option or is full house fumigation usually the way they do it? Thanks in advanced :)