There is a crackling sound that is produced by my PC when loading/processing, is there a way to quieten it?

If this just started to occur recently, it is likely your system needs to be defragmented. The noise you are hearing is sometimes called "thrashing" which commonly occurs when your system is attempting to retrieve data from fragmented hard drive. If your system has always made this sound, it could mean that your hard drive normally noisy and if so, you cannot do anything to change it except replacing your hard drive.