First, you do not have a Power PC Dual Core 2Ghz machine.
It would help if you could tell us what version of the PM G4 you have.
You can find that information Here and Here
I doubt that it is your hard drives that are making all that noise and I suspect that you have a PMG4 MDD (mirrored doors) as this is typical of that series when the power supply goes bad.
The noise you hear are the cooling fans running up to max speed.
If you have a PM G4 MDD, be aware that the power supply for this machine is EXPENSIVE!!
As your G4 is not actually booting, it will never reach a point where the keyboard input is recognized.
My hard drive died so I purchased 2 - 500 G Seagate hard drives - 3.5 7200.11. I have put them in the machine and now I need help formatting them and putting the OS 10.5.4 leopard on them. Actually I would like to use one as a storage drive.
First thing I noticed is that I can't get the optical drive open - usually that is opened on the keyboard. So how can I incert a disc? Is there something else I need to do first?
2nd thing I noticed is that the drives started spinning faster and faster (and louder and louder) as if it were going to explode at some point. So I thought I'd ask for help since I don't realy know what I am doing...
I hope you can help me get my computer up and running.