Unusual jaw shuddering

Hi all!

I have a mastiff x in which I rescued around Christmas last year. Just recently he has started showing unusual behavior with his jaw. It's much like a shuddering which can clearly be seen and heard. Similar to teeth chattering however the teeth don't meet. This behavior seems to come in waves of about 5-6 shudders with each shudder lasting around 3-4 seconds. The vet seems to think he appears healthy and has ruled out possibilities.

I found a dog showing the same behavior on youtube. This dog was treated for Eosinophilic plaque/Eosinophilic Granuloma which doesn't seem to be present in this case. The behavior however is pretty much identical and you can view the video by following this link:

https://www.youtube.com/watch?v=zSO1kQFFVdU

Has anyone else experienced this before? I'm just concerned as when it happens, my dog does seem distressed by it.

Thank you for your time,

Bunny