Note that this is also a heavily-filtered audio feed, meant to cut out loud noises because otherwise it would "blow out" the audio on the recording. It's not an accurate recording of what YOU would hear if you were in that spot. Also there are modern considerations now found in WW2 aircraft. How much sound does a hard shell helmet over your ears muffle now? In WW2 they had leather helmets and very basic ear cups. Many bomber pilots still suffer major hearing loss along certain frequencies because the protection was inadequate and all the noise came through. That's taboo this day and age, but back then? The technology was in its infancy and there was a war on. Also, the thin primitive plastic materials used for canopies back then as compared to now, the sound deadening capabilities of the same canopies then vs now.
I'm not saying you could hear a pindrop. I'm not saying you SHOULD hear other planes' engines all the time. What I am saying is that tank divisions made LOTS of noise. They were a creaking clanking and THUNDERING noise often heard for miles over the horizon by people on the ground. At low altitudes and with an engine windmilling, it would be quite loud and is very within the realm of possibility. Was it done? I don't know. I'm saying the possibility is there that if it was done, it would work. Same as with us flying planes with almost no fuel off the runway, or firing off 1000x 7mm MGs to lighten your load because you decided you wanted to turn fight better -- never done, but realistic and "possible."
Bolded the part which contradicts what you just said..... "meant to cut out loud noises".
Airplanes are loud....Radial aircraft are louder...sitting behind the engine in the prop blast at 300mph....
Here is another video...from a Go Pro.
Note no external noise heard...even the PA system at the airshow, or the Hurricane taxiing beside him.
And a home boy with his handycam flying shotgun with Blue Angels....
You can hear the jet exhaust noise when he is tucked in tight, otherwise its just the wind.....
If you listen close you can hear the air "rush" from G loading....7:50ish mark when he rolls 180 out from formation and then dives and pulls...