Cat sometimes dribbling/drooling

The other day I noticed some dribble dripping from one side of my cat's mouth. I wiped it up and it did not seem to continue. But every now and then I notice the same thing. In all other respects, he seems OK. He is eating, using the litter box, grooming himself, does not react badly if I touch his lips or hold his jaw. The dribbling has been only from one side of his mouth. I don't know if his tongue is bothering him since he's currently engaged in a good grooming session. He is not currently on anything thought I previously had been giving him 1/2 a tablet of Zyrtec to deal with a congestion issue. He hasn't had any Zyrtec since Friday. He does sound "wet", if you know what I mean with regard to congestion but is not sneezing or coughing (though he will snort sometimes). I am taking him to the vet tomorrow but I'd like to see if anyone has some insight or ideas.

Maybe teeth problem?

My cat drools when he's happy and he's missing one tooth. One time he was drooling continuously after we had a contractor using power tools, but catnip solved the problem.