Strange audible tone when I plug in my external drive

I have an external drive connected to an iMac.  Both the drive and the computer are about three years old.  The drive, recently, began producing an audible tone that repeats.  The drive is not recognized by the computer.  Any ideas?  Please help!

Sounds like clicking, which tends to be bad unless it’s caused by a lack of power, try to post the model number since some drives can be taken apart (Voiding the warranty) and placed on another external case without much of a hassle.

Thanks so much for the response! 

The model # is:  WD10000H1Q-00

The tone is not clicking as you mention.  It is a cadence, almost rhythmic tone that sounds like a warning of some kind.  I is not continuous.  Lasts a couple seconds and then stops for a couple seconds, then again over and over for close to about 30 seconds, then stops.  I use firewire, at least on that model, to connect to the computer. 

Any ideas would be very welcome!

The only thing I can suggest is to try the USB cable and make sure the power adapter is straight to a wall instead of a power strip just in case, then take the data out. If it’s still under warranty then call/e-mail WD for a replacement, if it’s not then that model can be taken apart and have the external enclosure changed, even to a non-WD case.