A scraping sound could potentially be a bad thing. Make sure you back up your important data just in case.
You can also download the Seagate Diagnostic tools and run a test on the hard drive... if you think it is coming from the HDD... the program has a feature called the "Acoustic Test" which will spin down the drive just like a power management idle condition. If the drive was the source of the noise then the sound will stop. If the noise continues, you can eliminate the hard drive as the source.
Download it from here:
http://www.seagate.com/ww/v/index.js...00dd04090aRCRD