Why is more noise less irksome to my ears?

Factual Questions
1

I’ve been wondering something about noise levels and my level of discomfort.

Why is it that loud noises are less annoying when they are amidst other loud noises? That is, someone yelling to be heard over the noise of a party… or the loud movie volume coming over the sound of people crunching popcorn, clearing their throats, and shuffling their feet… or someone talking loud in a restaurant full of people… all of these things are loud but bearable. Take away the background noise, and these sounds can be too loud for me. It almost hurts. But add in the background noise–in other words, raise the overall noise level–and the volume isn’t so bothersome.

Why is that? Is it the contrast between the background and the loudest noise that is so painful, instead of sheer decibel level?

2

I have a theory that noise only bothers you when you think you can do something to stop it. If you hear the faucet dripping, you think you should go and shut it off. If you hear the neighbor’s stereo blasting, you think you should go tell him to keep it f***ing down. However, if you hear the buzz of traffic by your window, you can’t do anything, so you just let it float by … that is unless you start thinking you should move to a quieter neighborhood, and maybe get a better job so you can afford the move, and maybe go back to school so you can qualify for the better job, and maybe …