The CPU shouldn't make any noise at all, as there are no moving parts in it. That scratching noise can be a couple of things. Since this happens when you open a program, it's probably the hard drive making noise. It could be your hard drive is about to fail. The noise could also mean one of your fans is about to go. I can only suggest taking the side off of your case, listen closely and try to localize where the noise is coming from.