all the documents merge ground loop noise and alternator noise together.

Right. Because 99 percent of the time, those two things are exactly the same. If you have a ground loop somewhere, then you will also get alternator whine.

Is it possible that the noise is coming from my power leads? or is that just for alternator noise?

I think you're misunderstanding the nature of a ground loop. Electrical wiring is not like a water hose. It's not unidirectional, so it's not like you have a "contaminated water supply".

Ground loops happen when some of the electrical energy ends up getting routed through the audio cables. Then every single electrical device on the entire system (car alternator, player hard disks, player CPU, cell phone circuitry, spark plugs firing, brake light turning on, air conditioner fan, everything) can be heard through the speakers.

Your job is to make sure the electricity flows exactly where it's supposed to, and no where else. This means you have to convince the electricity that the better route is through the proper power wires.