Its all really quite funny. At least it was to us here at MacRiot. There are probably several quite irate individuals reeking in remorse for not purchasing AppleCare for their MacBook Pro's because 'suddenly' there's no sound and the warranty's out.
Well, this article brings good tidings, that with minimal investment and a gentle hand, you can have your sound back on your MacBook Pro. Apparently the fuss about whether its hardware or software was unwarranted and in most cases the 'loss' of audio is due to a micro switch getting stuck.
There's a micro switch in the audio output assembly and the people who usually complain that they have suffered a loss of audio are usually individuals who have been using their audio output jack regularly. This is the same on the iPhone.
What happens is over time, the micro switch that toggles between internal and external audio output whenever you insert your earphones or external speaker input gets stuck and deceives Mac OS X into believing that the jack is still in the audio output port. Thus, Mac OS X continually routes all sound output to the audio output jack.
For MacBook Pro owners this is commonly characterised by:
Remember, we said "tinkle" not spraying into the jack like there's no tomorrow...
Following the steps above will give you a good chance of restoring your internal audio.