i suspect HDD is faulty as it is a bit noisy. Is it possible to take an HDD from another 7125 and use it to get the down copier running? Will there be any kind of software confict? just curious.
You can put any similar drive in, you just need to load the software, there is no need of using one specifically out of an identical model.
It likely won't work until you format and then load the firmware though (when using from another 7125), I would expect it to not boot due to incorrect settings/slight hardware changes/incompatible NVM settings etc.
Please note, that when I say likely, I do mean that, but only in such a way that there is probably more than a 50% chance it won't work right, and not that it can't work, or shouldn't be tried. It isn't a great idea, but it certainly won't do irreparable damage