This problem lasts for several months already (first on Ubuntu 13.10, not on 12.04. I get very loud cracking/popping sound from my right Asus K56C's speaker, I searched everything but could not get rid of it. Several facts:

1. There is no problem on Windows 8.
2. It has nothing to do with applications running because it appears even before login screen of Ubuntu. Also same problem if I boot from Live USB.
3. Muting sound will remove noise, but lowering volume has no effect.
4. Inserting any headphones, removes the noise.
5. If I disconnect power cable while there is noise, noise will always disappear, but only if there is no music playing. If I start playing music, noise again appear even with power cable disconnected.
6. Sometimes that noise disappears for 1-4 weeks, and then again appears for no reason and lasts from several days to weeks.
7. That noise is always the same, and

I tried adding tsched=0 to /etc/pulse/default.pa. Also tried this PositionReporting fix, with no effect. I also tried disconnecting all the cables and removing all electronic devices around laptop, but it has no effect. I also tried removing Pulse Audio, didn't change anything.

Would be great if someone has some real solution for this problem.