No loud isn't in itself an insult. But most of the other things said here are insulting.
Even the fairly mild and fair OP said "My eardrums feel like they're going to burst!" Way beyond "they are a bit loud aren't they?"
Some of the comments on here are appalling by any standards and hardly anyone except a few of us americans have pulled any posters up on it.
I ask again - why is this kind of comment ok?
American tourists where I live are spectacularly loud, and bellowing, space hogging and obnoxious. So much worse when they're in a herd.
It doesn't come across as confidence to me, just dickishness, and lack of awareness and care about everyone else in the world. They come across as very entitled and arrogant. Of course it's easy to stereotype people, but in general I have found this to be true.
No, americans - well white americans - haven't generally been subject to any systematic discrimination. Which is why I find these comments rude and offensive rather than something more sinister - although I might be wrong in that.
But then the British haven't been subject to any systematic discrimination either (and there is an irony in British posters tut-tutting about American imperialism but maybe you have to be Irish to appreciate that fully).
But I can tell you - lack of "systematic discrimination" aside, you wouldn't be happy if I started posting about "the British" the way people on this thread are posting about "the americans". Wouldn't matter that you have been top-dog for past few hundred years, you'd still think I was rude and stupid.