I turn off my PC and then after a while I hear a crack noise but have no idea where it...

[Lewis Collett]

I turn off my PC and then after a while I hear a crack noise but have no idea where it comes from. This had only started when I put my new RAM in yet my PC works flawlessly, any ideas on why the cracking noise happens? Is it a bad thing or is it nothing to worry about?

EDIT: I am not sure if it is either my PC or Monitor. My Monitor makes cracking noises but it is nothing to work about, it usually does when I turn it off after it being on for hours.