git submodule modified files status

I've added a submodule in my main git folder tree and haven't changed anything but it's showing up modified. What do I do about this?

$ git status
# On branch master
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#    modified:   example.com/soundmanager
#
no changes added to commit (use "git add" and/or "git commit -a")

I've tried a git submodule update, but it doesn't do anything.