How bad is the knock? Is it kind of like a hammer hitting an anvil? If so, you have to figure out which one it is (you should see fuel marks or black areas around it), remove it, clean up the whole thing, replace the copper ring with a new one (yes, I know you just put a new one in), and re-install it. Your injector is probably loose. It happens to the best of us. You really need to have a torque wrench when installing the injector holders (the pieces holding the injectors to the engine).
What's going on is that your injector is slightly loose, and due to the high compression of the engine, it bounces up and down ever so slightly.
BTW, welcome to the world of modding. I hate to say it, but nothing is 100%. It's a terrible feeling when things go wrong, but that's what can potentially happen when one starts changing things on the engine. Modding is definitely not for the weak of heart (or stomach).
I doubt that your injectors are shot. Just something loose. I had the same thing last year. I put injectors in, had them in for a week. No issues. Drove to Boston (straight...no stopping after Buffalo) and just outside of Boston I got the injector knock. Sometimes takes a while. After that scare I got a torque wrench.