The idea I have is that, on being triggered, each hard drive would start reading/clicking and then die out (doing less and less). This could be triggered over and over.
I also don't know what type/era of hard drive would be best for this type of work
It's called a VCM (voice coil module - don't ask me why)
Have you got a schematic of the hardware side of what you're working on?
Now I just have to find a sufficiently old/loud harddrive to make this worthwhile (modern ones are so quiet).