I think that it must be either the speaker itself, the soundcard, or the power cable running to it but it is definitely a hardware problem of somekind because it happens under OSX and Linux. My question is: will replacing the upper case fix this? I've found a few listing on ebay for the trackpad/speakers/uppercase for my model and it seems to indicate that the speakers are integrated into this component? Please let me know if this is correct and if you have had a similar problem/solution. Thanks!