Front door lock "clicks" after closing
if your door has a deadbolt and a passage handle, its probably the passage bolt, just popping into the latchplate recess.  this is common as you want the door to compress the weatherstripping and seal the door, but not have a load on the deadbolt as you try to unlock/lock it.  the passage bolt is just set so that it takes the spring load from the weatherstripping in order to unload the deadbolt.

if your door is just a standard keyed security set, it could be the anti-pick pin on the backside of the bolt just popping past the strikeplate as you put pressure on it.  if its not fully extended, the bolt is much easier to wedge in with the door being locked (so your lock isn't doing much from a security perspective)

if your locks are working fine and your door is sealing, i would just leave it be, if not, you can try experimenting with the strike plates.  moving them in and out even a tiny little bit can make big changes, negative or positive, in how the door works.  you might want to get a pro if its something you have never done before.  its very finicky to get it just right (and have it stay that way over a wide temperature and humidity range)