I have a little to add to this on the subject of noise protection, although related to aircraft, not to infantry.

In the ramp up to WWII, it became obvious that the mental and physical health of airmen was going to become a crisis. Better planes and the increase demands of an possible impending war were requiring more and more people to travel longer distances, at higher altitudes, for longer times, in cold, noisy conditions (think continuous engine noise), subject their bodies to sudden changes in gravity etc.

In Canada, at the University of Toronto, Frederick Banting (famous for discovering insulin), was aware of this and also aware that having better protected airmen would be an advantage in war. He founded a research team, drawn from his own Institute at the university, to look into 'Aviation Medicine' to develop better technologies for allied airmen. Among the people who started work at No. 1 Clinical Investigation Unit in Toronto was a technician called John Goodwin, who during the war worked on protection from aircraft noise. After the war, he continued to work in this field of noise and people, including, it seems, the psychological effects of noise.

I'm afraid that's all I can add as it only came up tangentially in other research I was doing about John Goodwin. This (page 86 for the article, 90 for the sentence on Goodwin) is the one publically-available article I have found that gives a good overview from the era, although with a bit of a heroic spin, I'm sure.

Sadly, nothing on work done to protect infantrymen.