Whirring Noise

I have a problem concerning a rather loud whirring noise which
happened about a week ago and lasted for about 30 mins. The
noise then re-occurred a day or so later. There has been no occurrence
since then. It is obviously a hardware problem. Any thoughts, please,
on what might be causing it ?

The system is Debian Jessie running on a desktop. I mention this
in case the system needs resetting if any hardware has to be
replaced.

Fan ?

CD/DVD ?

Hard drive ?