Any significance to head sounding like water in ear, when tap head?

I've been diagnosed with hearing loss and have worn hearing aids for about 5 years now. I have problems equalizing pressure in my ears after flights. I also have nasal allergies. About two years ago, after a long flight, I couldn't "clear" my ears. Eventually it subsided, but a few months later I just happened to "tap" the back of my head to indicate I was thinking, and my head "sounded" like it used to do after swimming when I still had water in my ear. What's the significance of this sensation, which remains. And is there any fix to it?