I have a mid-2010 13" MacBook running 10.6.8. For the past few months, my volume control has not worked properly. If I use the buttons on the keyboard, the volume stays the exact same, even when muted. The volume control on the top menu bar does the same, too. The only way for me to change the volume is to go to system preferences and change the sound output manually. Is there any way to fix this?