I believe that it is completely software related.
I ignored all these threads talking about speaker crackling sounds because I thought they just had a bad hardware copy. It doesn't pertain to me... blah blah blah..
I bought my $99 TP and overclocked it with F15c eagle up to 1.8GHz and never had a problem with audio crackling. NEVER!
BUT NOWW.... after upgrading to 3.0.4 I am getting this horrible sound crackling spontaneously! It's very annoying. Sometimes I have to perform a luna restart. Sometimes it just goes away after a few minutes.
What ever may be the cause, I believe it is software related.