In most cases, rattling noises are normal and are no reason to worry. They are caused by mechanical parts of the HDD and just indicate that the drive is reading, writing or calibrating itself. Even if the drive is not being actively written to or read from, most operating systems do a lot of accesses to the system disk in the background. So if there is no additional indication for a defect, just the noise alone basically does not indicate that the drive is faulty. And Toshiba might recommend you to consult PC/system vendors or the shop you purchased the device/system about the phenomenon since the HDD is just a part of the system.