Fan Noise

I'm having a slight problem with the fan cooling the CPU on my computer
Hewlett Packard 6712 with a 667mhz Intel Celeron processor.

A few days ago I replaced my CDRW drive with the original Optical CD drive
after it deveoped a fault, fortunately it turned out to be a loose wire in
one of the cables connecting it and i've now re-intalled it in the computer
and it works fine.

However...the noise from the fan seems to have increased dramatically...it
sounds like its going twice as fast. Its extremely distracting and it
definately wasn't like it before. I thought at first a wire may have come
into contact with the fan case, but i've ruled that out. Changing the CD
drives didnt have any effect on the fan when I installed them before, why
would it now? Can the computer automatically increase the fan speed?

I cant see any reason for the increased noise. Its driving me crazy lol,
anyone got any ideas?

Steven