An interesting thing I learned about while working on the wind turbine ordinance and noise is "learned aversion". As it applies to turbines, or guns too I suppose, if you don't like them, how they look, own a coal mine, or whatever, then the noise is much more bothersome to those people--even when they are hearing the very same noise as the people who are not bothered by it.
There is a real physiological stress response to this self-imposed aggravation that can impact health. But the stress is a response to the aversion, not the noise itself. Either way, it can cause high blood pressure and all the bad things that follow that.
I don't think guns have the same issue with ultra-low frequencies that turbines have. This is basically a sound pressure wave hitting you that your ears cannot detect but your body is still reacting to it. Even if guns did have that low frequency sound pressure wave, people aren't exposed to it over long periods of time compared to turbines.
Maybe LD1's neighbor could use a pair of sound-cancelling receiver headphones tuned to PBS? Whatever works.