Drive makes clicking and high pitched noise. Computer wll not recognize the external hard drive.

Are these G drives external?

Clicking noises are not an issue, as the hard drive uses voice coil technology, which clicks. Plug into another USB drive.

The spinning mechanism on the HDD is failing meaning it can't read data of the platans. Unfortunately you need to buy a new one as this one can't be repaired.

you need to install the software for this drive on your mac

one of two problems , the interface or the unit , first start by
removing the outer cover to make sure the unit is connected
properly inside , then when connecting make sure you hear
the plug in sound of the USB low to high , a high to low sound
means the there is a problem with either the USB or the cord
second make sure you hear a noise or see a operation light
if so reboot the computer while the unit is plugged in , look
for icon in my computer , make sure you hear a spin up sound
if the unit spins up and down the units motor is malfunctioning
if there is a clicking sound the units heads need replacing if
everything sounds and looks good try taking the HDD out of
its closure set the jumpers to slave and hook it up inside of
a PC to troubleshoot if there is a problem with the closure

Try the hard drive on another computer to see if it is the external or a laptop interface problem. There are EIDE/SATA to usb adapters that you can connect a hard drive to that the computer will then read as an external hard drive. The problem with external HDDs is the usb interface built into them, these are mounted on controller cards and that is ususally where the failure occurs.

High pitch noise usually means the inverter board that drives the lamp behind the LCD display. If the rest of the laptop appears to work, for example, hard drive light blinking while booting, try hooking up an external monitor and hit whatever function key that switches you to the external monitor. If everything works, you may want to replace the inverter board yourself. It is not horribly hard if you are very careful. But it is not exactly a walk in the park kind of work.

If the rest of the laptop does not appear to work, the DC-DC step down power circuit is probably shot, which will also make a high pitch noise. In this case, you will have to replace the motherboard. Replacing a motherboard is a major pain in the behind. In most case, it is not worth the trouble if you have an older model.

it happens when the hard is gone bad or can`t be recognised.you can try uninstalling the drive from device manager.you can check the hard drive case or can try the hard drive on some other computer.

There is some hard ware problem for this physical site visit required.

There is a chance that the hard drive itself is at fault and the computer cannot recognize it try using it as a slave drive in computer. and use a recovery cd from boot to check it out
You could use thee ultimate boot cd (download) to check it