It’s really very hard to say “what the Northern Lights look like”, because they’re different each time. I’ve seen them a total of six times, in five different forms:
The first time I saw them, the whole sky was changing colors more less uniformly: It would be all red, then fade into all green, then all purple, etc. Occasionally, there were thin lines of white light that moved across the northern sky, like windshield wipers.
The second time I saw them, it was green amoebas. There would be a blob in one part of the sky, which would change shape, and grow and shrink, and occasionally fade out and re-appear elsewhere.
The third time, there was a pale white arch over the sky, which turned into a pale green as my night vision kicked in. As time passed, it developed into the wavy curtains that you see so often in pictures.
The fourth time, there were spikes of pale greenish-white light coming up from the northern horizon, but which didn’t do much. I’ve heard that this is the most common type in my area (southwest Montana/Yellowstone).
The fifth time, it was curtains again. I saw them a bit later than in time number 3, so I didn’t see if they started out as just an arch.
The sixth time, there was just a vague glow across the entire northern horizon, just enough to silouette the mountains. There was a dark diagonal stripe through it, and above it, a reddish rectangular area.
As for the sounds, there’s no known mechanism by which they would be produced, and there seems to be a pretty good corellation between the occurence of sounds and the consumption of various mind-altering substances. Draw your own conclusions.
For the best time to see them, you want sometime shortly after midnight, a couple of days after a major solar storm. There’s websites and mailing lists that will tell you when these occur, but I don’t have any of the addresses handy. We had plenty this past year, what with the solar maximum, but that’s winding down now, so you might have to wait another eleven years. The most important thing, though, is to be able to get as far away from light pollution as you can: A good rule of thumb is that if you can’t see the Milky Way where you are, you probably won’t be able to see the Lights, either. Of course, it also helps to get further north, if possible.