Yes, that’s the issue on those occasions but it rarely affect both ears simultaneously, in my case.
I went back to the thread where this discussion started and saw @komemiute’s edit.
That seems like a good, low level, explanation.
When googling this the google AI will come up with this reply:
Yes, air density does affect the perceived volume of sound, though not in a simple, direct way. While sound intensity, which is related to volume, is roughly proportional to air density, the relationship is more complex.
Now, Google AI will also tell you that there’s no water in the swimming pool on the Titanic. So I guess that should serve as a caution. But following a link that Google used for the answer, I read this:
Quote from the article:
So in the scenario you’re describing, if T is taken as constant, then the speed of sound doesn’t change, but its intensity does, as the density of the air is much lower on top of mountains, rough approximation for the intensity would be
I∝pv∝ω²cρ
Where v is the speed of air molecules, ω sound frequency. So one thing is for sure, you will need to shout much louder on a mountain, for people further ahead to be able to hear you.
There’s also a reply debating this in what I think is more along @sobek’s explanations.
Reading further I come to think about the sounds @BeachAV8R heard… Engines with propellers and fans. Would speed of sound explain the muffled sounds? It’s colder at altitude, so SoS is lower. Are shockwaves forming on the tips of the propeller or fan blades, altering the sound image? Chris has heard more than an occasional aircraft engine in his career and I’m guessing that most of them are at warmer temperatures…?