Cat mouth breathing and weird clicking noise?

Signalment: Cat, American Shorthair, 8 years old, male, neutered, 11lbs.

Clinical signs: Mouth breathing, clicking sounds from mouth when breathing or sniffing (not constant), occasional coughing fits (1-2x per week) which the vet said was "reverse sneezing"

Vet reports: Don't have link to them, but he recently had his yearly bloodwork done and nothing was out of the ordinary. They said his lungs, heart, and teeth were all good.

Location: Wisconsin

Diet: Eats Acana Indoor Entree and has for years now, no prior signs of food allergies

Video of the weird sound: https://imgur.com/a/n5mb9UC

My 8 year old boy has been exhibiting these weird breathing symptoms for about 4 months now. The sounds aren't constant but occur on and off throughout the day.

I've taken him to two different vets and both say his lungs sound fine and that there's nothing to worry about. They said to give him 5mg of Zyrtec a day, which I've been doing for over a month and have seen no noticible results with. This video was taken a few hours after his daily Zyrtec dose.

He also has a history of having occasional coughing fits. I showed a video of one of his fits to the vet and they said it looked and sounded like reverse sneezing.

Other than the things listed above, he has high energy, has a good appetite, has regular bowel/bladder movements, and no mobility issues.

I can't shake the feeling that something is wrong, because there's no reason for him to be breathing like this even with daily Zyrtec, but the vets won't take me seriously.

Any ideas on what it might be so that I can bring it up to the vet? Thank you!