Though I am reluctant to go there, are you sure you are not experiencing aberrations in your hearing?
Consider your age and your circumstances. If you are exposed to very loud music, or if you are a shooter of guns, or if you work in a loud industrial setting then that could be an indicator? Being on the high side of life, and having experience way too much Rock-n-Roll, and having shot guns for years with no hearing protection, and having worked in industrial settings, my ears are shot. They haven't stopped ringing in 40 years. A young man's folly.
Though I'm not completely sure this will work, next time you hear the shift, try turning your back to the speakers, and see if the weakness follows your ears, or if it stays on the same speaker.
Last edited by bluewizard; 09-18-2019 at 10:18 AM.