Mostly what you hear is the sound of the pumps and fans that circulate air and water through your suit. It's not terribly annoying or anything, but it's not the silent lonely environment with no sound other than your own breathing like often depicted in the movies.
Plus, you are wearing a headset so you have the sound of your crewmates and the folks in Mission Control talking to you fairly regularly.
It is true, however, that sound cannot travel in a vacuum so you do not hear things outside. When you drive a bolt or tap a piece of equipment with a tool, you don't hear a thing.
One interesting thing that happens is that when you put your crewmates in the airlock to perform an EVA and then shut the hatch, at first you can hear a bunch of clanging as their metal tools softly strike the other equipment, handrails, or the hull of the small airlock. Then as you depress the airlock it still looks exactly the same through the hatch window. But now the clanging sound is gone. You can see their equipment bumping into stuff as before, but now it is silent.
As an EVA is in progress, you can hear the spacewalkers bumping and clanging along as your crewmates translate on the exterior of your module. It sounds kind of like ghosts in the attic dragging chains. Although without the scary moaning sounds!
And one more thing: As Stephen Colbert and I proved, it is true that in space, no one can hear you scream. Check out the link to our interview so you can see for yourself!
More questions on Astronauts:
- What is it like to live in space?
- What would astronauts do if their faces itch when they're in spacesuits?
- What's the typical daily schedule in the International Space Station?