My Book Studio LX spinning down during use

I am seeing odd behaviour from my My Book Studio LX hard drive connected to my Mac. It’s a few days old, being my third warranty replacement in a row (the other two replacements were faulty!). After heavy disk activity it stops responding, then spins down. i have to wait almost a minute before it spins up and I can access my data again. This has happened three times in the last twenty minutes. Is this a sign of a faulty drive, or something else - overheating - perhaps? I am worried that this drive is too going to fail.

You can always test the drive health on disk utility