Head gasket problems

If it's liquid dripping and not white smoke, you're likely seeing one of the byproducts of the catalytic converter. There should be a tiny drain hole in the back of the muffler where water will also drip from. The clue is the coolant level will not be dropping over time.

You can also add a small bottle of dye to the coolant, drive for a few days, then check at the tail pipe with a black light. If you're seeing coolant there, the dye will show up as a bright yellow stain. If you have to pull the heads to check for leaks, that dye will often show up there too.