Noisy Processor while reading....

Can't quiet this noisy box down, any ideas...I have a Pentium ll which works well but, it's noisy enough to drive someone to distraction...

When it starts up,or if you open a program it sounds like there is someone drumming their fingers on the inside of the box...any ideas, how can I once again get this thing to be quiet as it was when it was new...as I said it works well...no other problems. Thanks.