Any ideas?

Sounds like water pouring through a pipe coming from behind glovebox--possibly behind the firewall--when I drive the car. Can't find any evidence of a leak, but still worried.

 

The only fluid back there would be condensation from the A/C. The heater core is centered in the dash and could make a dripping sound if it was leaking from the pipe connection. Does it smell like antifreeze? It would not hurt to pull the under pan from the passenger knee bolster and pull back the carpet on the drivers side to check.

Also, check your radiator fluid level. If your sensor is not working and the fluid is low you could get a gurgling sound in the cabin.

 

Its the heater core as antifreeze passes through it. Pretty normal for most automobiles when vehicle is not completely up to operating temps and thermostat is still mostly closed.