Is your computer a laptop or desktop. It could be a overheating issue. Now when does this usually happens, I know you said random, but may be it does this while running a particular program. Also give us the specs of your machine for us to help you out as well mate.
yes overheating is a main suspect,dust inside your case can also cause this behaviour so do look inside your pc to see if thats the case.also whilest in there see if there is proper coolin ie fans working etc.
try to track where exactly the noise is coming from when it freezes.according to what you telling me sound like its coming from HD,if you can track it down and find it coming from HD than you have a winner.Good things with HD's is they dont always die brutally just like that,it will always make a noise(like a spinining noise) untill one day...shame sounds so sad...he dies
see what you can come up with and drop a post