If you harddrive has "S.M.A.R.T" it's supposed to give you warnings on startup or during use if the harddrive "thinks" it's going to run into problems. However, even though I have harddrives that support that, I've never seen it in action before a hard drive failed.
Usually it'll come out of the blue, but sometimes is proceeded by WinNT/2000/XP blue-screens, VERY slow disk access and strange noises coming out of the hard drive. If you get CRC errors, you're probably in for much worse.
The "clunking sounds" are a pretty good indication, so if you hear anything weird, back up your most important files ASAP. I've never heard of the freezer harddrive trick, it sounds dangerous, but I'll try it with some of the hard drives from my "junk" pile...
