If it's always been like that, may just be how the drive is mounted or a quirk of the case design. If case, the side panels may be resonating at the relevant frequency. Old hd drives were a lot noisier and on an early PC case I applied damping (on the inside !) using a small sheet of roof tar/aluminium foil that had been left by some builders. Probably piece of rubber or even timber glued in would help.
fihart, thanks for the reply. My HD (Seagate Barracuda ST3250410AS 250GB 7200 RPM SATA) is just over a year old. It has always made this type of noise so I wasn't sure if it was normal or not. I've never had any issues with the drive, other than the noise.
I don't know. If I had a drive that I even thought was making grinding sounds, I'd back everything up and replace the drive immediately.
jsc, thanks for the reply. I do have an external back up HD (acomdata PureDrive 500GB External HD PDHD500USE-72). This is just over a year old as well. I bought it about the same time I bought my SeaGate. I'm not sure about replacing the internal HD, since the only issue is the noise, which I'm still not sure is just a normal sound the drive makes.