If your computers sound works ok via external speakers / headphones then this issue is not related to drivers and is actually due to the speaker issue seen in this flickr page.

a guy fixing it can be found here:

http://www.flickr.com/photos/anachrocomputer/3505252488/in/set-72157617651181775/

This means that your speaker does not have enough space to move and is vibrating against the top of the keyboard bezel and is resonating.

Thanks,

John