I once added added a second HD all of 80 Mb ! ........ Yes it was that long ago.
The thing uttered a thin high-pitched squeal shortly after switch-on and lasting about a minute.
On its own, as sole HD, there was no noise. I was uneasy and eventually sold it on while it still worked and didn't bother the new owner.
I can only guess at a imperfect bearing and a resonant sound generated in the peculiar mechanical conditions inside my case.