@donjo
Welcome to Mayo Clinic Connect!
I’m sorry you don’t have an answer yet to this annoying problem.
It reminds me of my husband’s problem. For quite a while he has had a similar problem. He also had an endoscopy that was all normal in addition to having normal pulmonary function tests.
His primary care doctor recently put him on asthma inhaler- combination with an inhaled corticosteroid- as a trial.
He has noticed an improvement now after a couple of weeks.
Maybe something to discuss with your doctor?