A very confusing way to put the question.
I can't figure out which fan is making the noise? Was it the CPU fan that you changed? But if it wasn't making any noise why did you end up changing that?
If it was the rear fan that was making noise , why didn't you change that?
Now that you've changed the CPU fan , which fan seems to be making the noise, the CPU fan or the Rear case fan?
What way is the air being pushed by the rear cabinet fan?