One of the best feelings in the world is to ride without a helmet. I don't care how dangerous it seems, it's more than worth it. For the first 4 years of my marriage, we didn't even own a car -- had to get one when I got pregnant, though.
The sound depends on what kind of bike you're on, and how fast you're going. On an old chain-drive Harley, you get noise; on a racy little Triumph it's different; on a VERY old Honda 750, it's like riding in a VW without a body on it.

I'm only pointing that out, because if the bike's loud enough (& loud pipes DO save lives

) you won't notice much wind-noise, but on the '69 Triumph I noticed the wind a lot more. I wouldn't really say "thunder" or "roar" about the wind -- think more along the lines of a communing with nature or another spiritual experience. Unless your character doesn't like it -- then anything along the lines of "terror" will work, or so I've heard. It's totally different on the front -- there's a reason a lot of bikers have big forearms, unless you ride like an old lady you're holding yourself on against the wind the whole time. Can't duck behind someone for a break.

I'm tall, so I had to duck to get a break, even after we switched my seat to a p-pad.
Combing your hair out after a long ride isn't as difficult as it sounds, if you have straight hair. Sometimes I wouldn't even braid mine -- just wear a bandana-headband and sunglasses. The only problem, is that over ~50mph, the ends'll whip the hell out of your face if you don't have a windshield (sometimes we rode with, sometimes without) or if you have a strong wind blowing across the road you're on. You absolutely, positively, 100% of the time need something covering your eyes. For bugs, but also rocks, and you would NOT believe some of the $hit dumbasses throw out of car windows. If you're squeamish it can be gross to wash the bugs off your face & neck when you stop.
If you have any more specific questions, let 'er rip. I love reminiscing about this stuff!