There are many reasons why a HDD might make more noise:
- Heavily fragmented
- Significant bad sector remappings
- Application demand
I'd first assess the health of the drive using something like HDTune
and look at the SMART values.
Then I'd run some defragmentation utility. The defragger provided by Vista and 7 is ok. I'd just use that in the mean time - there are better tools out there but we don't need it to be perfect.
There are certain background processes that run on windows that can cause additional hard drive activity. Do you have indexing enabled?
Regardless of the scenario it's a good idea to back up your essential files to an external drive / USB key.