Just to throw my twopennyworth into the mix here.
A lot of Audio, crackling noises can also be caused if you are overclocking and using software utilities to enable this, such as EasyTune 6 or AMD overdrive.
If you are overclocking your system it is a much better idea to actually make the necessary changes to your system from within BIOS. This has the advantage of your system starting out in an overclocked state and you can remove the overclocking software that very often causes more problems then it solves.
Audio, especially if you are using the on-board sound chip can be affected by the increased voltages, running through a motherboard when you overclock. In fact, even if you are not overclocking the audio can be affected by the natural changes in voltages and frequencies passing through the motherboard, especially if you have energy saving features enabled. It is often better to disable the on-board sound and add a 3rd party soundcard to eliminate this problem.