Like people, dogs can also have some annoying habits. And there were two that baby Huxtable was acquiring around 3.5 months-- licking too much and smacking. The latter is one of my biggest pet peeves with humana, so of course when my dog started to "smack" "smack" "smack" at random for minutes at a time it got pretty old pretty quick.
I first did a quick search for dog smacking, and dog smacking lips-- everyone said it was normal, and to ignore it. I'm sure it is normal, but he was doing it so much I knew that there had to be more to it. So I began to observe his actions more to see what actions he would do before smacking alot. One of things I found him doing was licking clothing and fabrics before going on a 15 minute smacking spree. My clothes (when in my lap), blankets (when laying on one), and towels (when laying on one), were a few of the items he end up licking sometimes. Besides drying his mouth out, I began to think that the detergent or soaps on those items may have thrown off the "ph balance" or messed with the "good bacteria" in his mouth. So after trying water to no avail, I began to think of what I could give him that could help... and I just so happened to have a whole bottle of plain kefir milk in my fridge that I was using to restore good bacteria, and put live cultures in my own body. But before giving it to him I wanted to see if it was safe for him to digest. I ended up reading a thread about a woman who would let her poodle lick the spoon and bowl when she made fresh kefir milk, she spoke about how much her poodle dog loved kefir milk. So I decided to give it a go.
After letting him lick a teaspoon of plain kefir milk he stopped smacking, and of course he loved the taste. (He licked the spoon over and over again). This worked a few other times for me when his smacking became unbearable. Not sure if this could work for all dogs or even all poodles, since many dogs are sorta lactose intolerant, but this seemed to temporarily do the trick for Huxtable.
If "lip smacking" isn't normal for your dog then there are likely 1 of 2 issues going on: 1.) he has a bad taste in his mouth 2.) he may be teething
Just be sure to be as observant as possible whenever oddities or new behaviors occur with your puppy, with a little thought you'll likely be able to deduce the cause of the problem.