Go to the Seagate website and download their disk testing utility package, Seatools. They have several versions. I prefer the one you use to burn your own CD-R containing all the tests. Then you put this disk in your optical drive and boot from it. It loads a mini-DOS into RAM and gives you a set of menus to run all tests completely independent of your regular OS (Windows). Run the tests and note down any error results it reports. It may offer to try to fix a few things for you. Then discuss with Seagate Tech Support - they can advise whether the unit should be returned for replacement under warranty.
Thanks, I'll give it a go and post my results.