Loud licking/backwash noise at night.

I have a shihtzu mix who is 7 years old. I’ve had him since he was 11 months. The last few nights he has been driving me crazy with this loud mouth licking / backwash sound. Its sounds like he’s licking through soft peanut butter that stuck on the roof of his mouth. It’s so loud he wakes me up in the middle of the night with it. I have brushed his mouth out and made sure he’s drinking water. He only does this at night and it’s getting to the point where I’m gonna have to put his bed outside of our bedroom and that makes me sad. I just wanna sleep, preferably with my dog next to me! Does anyone know what could be going on?