Hello Guys,
I have late 2009 edition. When I uninstalled El Capitan and installed Ubuntu, the sound worked perfectly. Now I have removed Ubuntu and have EL Capitan but still did not work. The problem is definitely El Capitan. If it was a hardware problem, my Ubuntu would not have worked. I tried all the suggestions I found online and followed them to the letters but nothing worked till now.
MacBook, OS X El Capitan (10.11.3)