I also went through physical therapy too. I hope you're past any pain and are doing well. I know how painful things can get.
>It feels very possible that some forms of meditation may not necessarily be about utter quiet, but rather such focus that noise cannot exist.
You might already know this, but meditation is about identifying when you are and are not in the present moment, be it quiet or not.
So utter quiet isn't necessary. There are thoughts in the present moment. The present moment is when you're aware of your chosen anchor, eg the breath. There are noises sometimes. One of the first kinds of meditation I did I was told to listen to the birds outside. If my mind started taking me away from the birds, I went back to listening to the birds. The goal of meditation is to identify this transition from the present moment to away from the present moment, and back.
There are many kinds of meditation, but usually when someone says meditation they mean concentration building types like Mindfulness Meditation, which deals with learning how to identify the present moment. Absolute quiet is a misunderstanding, though it is nice when camping.
In ancient eastern practices (where meditation comes from) there is the concept of a middle ground, which isn't moderation. It's basically: do what works best in that set and setting. If amphetamines work for you right now, then that is your middle ground, but know they will not always work on everyone the same way.
Eventually if you exercise your mind, like exercising a muscle, you will need less and less of the drugs you're taking to be able do what you want to do. I have ADHD and was amphetamines too, but after I started meditating for a while, my concentration jumped up and I ended up having to take less and less meds until I stopped taking them all together. Of course, I can still take them, but it's nice that meditation lets you hack your brain and change your mental state to what you want.