I just bought the same drive from NCIX (read there forum for this drive this is a common problem) From the getgo the drive made this clicking noise, randomly every few seconds. I contacted Seagate they say it is a sign that the drive is failing. Seagate says they have no knowledge of problems with this drive but if you check here you can see it is very common. http://www.ncix.com/products/index.php?sku=27144&vpn=ST3500320AS&manufacture=Seagate check the forum at the bottom of this page.
I am now trying to get Seagate to replace the drive.