Expansion of the water as it heats would be my thinking. Water expands about 4% in volume when heated from room temp to boiling for example. Once the pressure on your lines and faucets equalize, no more dripping.
No big deal, but you could ad and expansion tank if it really bothers you. The expansion tank would also let you pull a little water without the pump kicking on or pulsing. Although if your water pump is a variable speed pump (VSP) they do not recommend using an expansion tank. If you add a expansion tank, there are RV specific models made that are small, but if you have the space for it, there is no reason not to use a "regular" expansion tank from HD or Lowes, etc.... The larger tank will go longer between pump runs as it stores more water in the tank.
Just the 2 of us in a...
2015 Freedom Express 246RKS
2002 GMC Sierra 1500