I don't think it would hurt to try a little vinegar in the water (any kind, because ACV isn't really all that special), and/or a little lemon juice or cayenne pepper. This isn't a typical symptom of a bacteria or yeast problem, but you never know.

I suspect that the main effectiveness of these remedies has to be in the crop, where there's food sitting around waiting to be processed and not a lot of digestive juices to interfere with the microorganisms that are enjoying the food. Later on in the digestive tract you have stuff like hydrochloric acid, which is a LOT stronger than vinegar and should take out any nasties that don't like acid. But there doesn't seem to be a lot of acid in the crop unless we put it there through the food supply, so it's a prime location for microbial infections.

I'll try to get a video of it so you can see what I'm describing.

It's sort of dark. Poppy is in the back.

Huh, that is odd. He's still eating and chewing on stuff like before? I have no idea what to make of it, but if it were me and if he is still eating and otherwise acting normal (normal poops and whatnot), I'd wait it out for a week to see if he just stops.

Wow. That's even more strange than what i imagined it to be.

It doesn't look like a crop-settling motion to me. I think he's just opening his beak, not trying to achieve anything. Maybe he gets some entertainment value from it. He acts healthy.

He is healthy, I've just never seen a bird do that before. I'm not sure he gets amusement from that, at least not that I can see.

Is it a neurological thing perhaps?

Stephanie, he does the same thing Mr Darcy does most of the time. He does it just because he likes to do that when he's near other birds, sometimes they start doing the same for a while then get bored and stop.
I call it the silent old man gumming lol.

I will show you a video soon and you'll tell me whether it seem like the same thing to you.

Very odd definitely not yawning! LOL
At least if Barbara's tiel does it too
it cant be much to worry about hopeful....
Maybe ask the avian vet, you can always take the video for him to see...