why is water collecting underneath the vegeatble trays?

I checked the drip pans and behind the fridge for leaks.....nothing (completely dry)! Water is collecting underneath the veg. trays on the inside of the fridge. It's driving us crazy. Every couple of days I'm using a turkey baster to suck up the water....a real pain in the you know what!! What else can I do? I'd really appreciate some advice.