Dead HD spinning and making noise

I'm planning to replace the internal HD in my Powerbook G4 laptop, and already have what I need and instructions from iFixit. This drive cannot currently be recognized or repaired by Disk Utility or Disk Warrior. So I hooked the machine up to an external, which has mostly been working fine for quite awhile. But lately the old internal has been sporadically spinning and making lots of noise. This happens at startup or other times and stops when I close the lid, or just stops on its own. But one time, it started with the lid closed, which freaked me out, so I've been just shutting down more when not using. My main concern is, does this normally happen with an old non-functioning HD that is still installed, and am I hurting my machine by running it this way? It is quite nerve wracking, but it's hard to find the time for the replacement attempt.

Thanks for your helpful responses. I've already decided that the internal HD is done for, and when I get it out, there's an option for someone besides me to try to recover the data. Most of the data was not sensitive and could be recovered from other formats, I just lost some photos I'd rather not have. Backing up the old drive at this point is impossible, as the system won't even recognize it, though of course it would be nice to back up the external I am using now.

I'm glad there's only a SLIGHT chance I could damage the machine by running it with this wildly spinning, useless HD. But I will heed that warning and create a space for the work ASAP. I have put it off not only because of time and expense, but because I have never replaced a HD before, let alone in an aluminum Mac laptop which I love and do not want to screw up! For budgetary reasons, I must do this myself. I have good manual dexterity and have obtained the new drive and the proper tools along with printing out the explicit instructions from iFixit.

For a long time after determining this drive was dead, it made no sound at all, and this problem is quite recent, another factor in putting off dealing with it. It is getting more persistent and annoying, but it just stopped.... ahh, silence is golden!

Thanks again, and to iFixit for hosting this great forum and providing such great Mac repair resources online. And I'll probably ask some questions about non-computer items. You are awesome.

I'm a woman and will try to post a photo soon.

Anne