I don't really know how common it is, but I know somebody else who told me they have the same problem. I actually hear sounds pretty vividly.

Have you ever made a conscious effort to hear things in your dreams?

Maybe what you could try, is in your next few Lucids, make it your task to listen to stuff. focus on listening to anything around you. Maybe even try picking different things up an banging them together. Or even try talking, shouting, singing, or whistling to see if you can hear yourself.