sounds like dripping water

I'm in a three year old house on a concrete slab. The PVC pipes come up through the slab. When I run the hot water in the bathroom sink, and after I shut off the faucet, I hear a water dripping sound about two feet above the sink and about two feet to the left of the faucet, behind an eight foot mirror. It sounds like water dripping on metal. There are two sinks, and it appears to be happening with only one. I believe the house is all wood framing. I cannot see where the pipes are going because of the pre-fab cabinetry. Any opinions? Thanks for your help!

That "dripping" or "ticking" noise is normal in plastic drain pipes when you drain hot water through them. It's caused by expansion and contraction.
Don't worry about it. Plastic drain pipes are just noisier than metal.
Mike