I've had this problem off and on for years. I have allergies, so always assumed it was related to that. Nope. This past year, I discovered I also have a thyroid issue, and ETD can be related to hypothyroidism. Well, even on thyroid hormone I still had the ETD.
So I've been researching the web constantly, because my ETD is so annoying. I have to yawn or swallow constantly or else my ears feel clogged and when I speak, it sounds very muffled. Sometimes even clearing my ears doesn't help. At it's worst, I couldn't clear my ears at all.
I've gotten relief for a lot of my other thyroid symptoms with vitamins and minerals. The research shows that a low thyroid can cause you to be deficient in a lot of different nutrients do to malabsorption and inability to metabolize and convert vitamins into their active forms. Specifically, you do not convert beta-carotene into the active version of vitamin A that your body uses.
I started hunting around for research related to eustachian tube and vitamins, and found nothing about humans, but eventually I found some for animals. And it was all about vitamin A deficiency.
In the ear, air is constantly being lost from the ear cavity through the soft tissues of the ear, by a process of difussion which isn't well understood. If the soft tissue lining the ear cavity is too thin or too porous, you will lose the air a lot faster than normal. I think this is what is happening for many of us with ETD. Also, the eustachian tube itself may be sticky, due to the lining of the soft tissues being compromised. Vitamin A is needed to properly make the epithelial lining of your soft tissues in your eustachian tubes, your ears, your nose and throat and your eyes (and probably everywhere in your body). If you don't have enough, your soft tissues get scaly and dry, inflexible. In your ears, that means your eustachian tubes get stuck closed (or maybe stuck open too!) and also the air is lost faster from your ear cavity, causing pressure changes faster than normal.
I found a retinal acetate 5,000 IU vitamin supplement, and started taking that every day and it worked immediately the first day, and has kept my ears clear the past three days! I know that isn't very long, and maybe I'm celebrating too early, but after dealing with this for so long, three days of not having this problem is too wonderful, I had to share my discovery.
Hope this helps some of you!
P.S. I also take a low dose zinc and copper supplement. Zinc helps you move vitamin A around the body. Without sufficient zinc, you will not benefit form taking vitamin A. And copper is important to take with zinc, and is also important for the building blocks of soft tissue.