@chasmayhear I didn't realize they had a name for what your are calling Valsalva maneuver. It seems to be the same as when you sneeze but don't want anyone to hear it. I never hold a sneeze back, but I have "popped" my ears. Yes, it improves the hearing, but it's only temporary and not limited to the high frequencies. Maybe you'll get a good response in the ENT forum??? A blocked Eustachian tube is one cause but there are probably better solutions. Another cause could be the muscle that attaches to the eardrum. It's the ears self-defense mechanism to try to prevent damage. It helps to limit the amount that the eardrum can move. Let us know if you've gotten any additional information.
Tony in Michigan