700mhz ibook "hoots" upon startup

Question

ibook "hoots" -- a steady musical tone about 4 seconds long -- then chimes and starts up. Everything seems normal but I'm worried something is going bad in a big way and I need to replace it right now.
The hooting has been intermittent but now seems pretty consistent upon every startup. Genius Bar no longer runs diagnostics on this model.
Help! This little ibook has been a trusty workhorse for ages. Maybe it needs to be put out to pasture on Low-End Mac. Thanks.

Answer 1

Again, I have heard of similarly described tones which occurred prior to hard drive failure.
I wouldn't merely accept the hard drive verification. I would want to repair the hard drive. The easiest way to do this is by booting into Safe Mode. This will take quite awhile longer than a normal startup because it does a file check and repair of the hard disk.
You will see your normal desktop. Once completely started up in Safe Mode, restart normally, and go to Applications > Utilities > Disk Utility. Click on the top hard drive icon in the left sidebar and again note the S.M.A.R.T. status at the bottom right of the pane to confirm again that it is Verified.
Select the named boot volume in the left sidebar ("Macintosh HD" unless you've renamed it). What is the hard drive capacity and how much space remains available on it?
Repair permissions on it (again).
This will allow you to see if actual hard drive repair silences that alarm (at least for awhile).
Good luck.