I just bought two 2TB Toshiba hard drives. They are both brand new and have been used for less than 24 hours. One constantly makes a very quiet but abnormal noise even if only the power cable is connected, while the other is dead silent and only makes noise when it is actually in use.
Here's a video clip demonstrating the sound with a microphone put next to the HDD. Please note that at around 49-54 seconds a loud series of clicks occurs - this is the microphone's coil cable rubbing across my camera's body.
sounds like in shipping the drive got dropped. i would run hp tune and check to see that the firmware the same on both drives before you start the rma. sometimes firmware fixes can fix buggy issues with drives.