Hi there - I finally settled on these instructions at:
http://mymacfixes.blogspot.com/2009/06/how-do-i-stop-clicking-noise-from-hard.ht ml
seems like a step-by-step but some knowledge of what you are doing is presumed (as per usual). I didn't get anywhere with the hdapm link on these instructions as it downloaded as a "package" which I then auto installed, only to find I just ended up with a daemon but with all the wrong settings in it -which took a while for me to get rid of! I eventually went here and downloaded this one:
http://mckinlay.net.nz/files/hdapm.dmg
you can tell it's the right one as when you have downloaded it and clicked to mount, the .dmg you will see in Finder contains a little file called hdapm, plus hdapm.plist plus a read me text file (not a package) - it's this hdapm file you copy to where the instructions say.
You will need this (as it says in the instructions):
http://sourceforge.net/projects/lingon/files/Lingon/2.1.1/Lingon-2.1.1.zip/downl oad
and when it briefly says "With Lingon, create a new launchd configuration file" it just means you press the "plus" button on the menu bar for a "New" whatever the **** a "launchd" is! Then just follow the instructions as they will make sense when you are in Lingon doing it. As he says you can see what your user name is (for where you type "com.yourusername.launchd.hdapm" and replace the yourusername bit) as it is displayed in Finder on your Mac next to the little house symbol in the sidebar.
Best of luck - don't do it at 1am like I did, although I must say I slept well after a successful install 🙂
PS. all the bits about "authenticate" really through me, where? how? when actually all he meant was you will get asked for your Mac password at some stage so type it in to proceed!
Tim