Try the DriveSavers hard drive demo app, if you have an iPhone or iPod touch - it provides examples of the different types of sounds a failing hard drive can make:
http://www.drivesaversdatarecovery.com/ep/drivesaver_app/
You probably won't hurt the PowerBook, and the internal drive is already done for, but there is the VERY SLIGHT chance of the bad hard drive damaging the controller on the logic board. You will probably will make yourself feel better by removing the bad drive :)