Excessive drooling...

Doc started excessively drooling yesterday. The sides of him nose and underneath and down his neck is all wet and you can see strands of drool hanging down every so often. This is unusual and sudden. I've checked his mouth and teeth for anything unusual and don't see anything. He hasn't vomited that I've seen. If it's still happening tomorrow, I'll call the vet, but, in the meantime has anyone else experienced this and know what the problem could be? He's eating and acting normal in every other way. Sore throat maybe?