It makes a slow whirring noise when it's starting up.
As Keef suggests, it could be a cooling issue if the whirring is coming from a fan. But it could also possibly be coming from the HDD - although the characteristics of the noise and whereabouts it's coming from might rule this out. But scanning the disk surface will do no harm and may show up a failing HDD.
Right-click on the drive in Explorer and select Properties, select the Tools tab and click on Error checking/'Check now' - select the checkbox that is not already checked (the one about scanning and attempting to recover bad sectors) and set it going. The results are fairly self-explanatory as I recall. If it tells you about having to recover data from bad sectors you've probably got a failing drive.