Wow, you seem to be bouncing around a lot.
First it sounds like lifter rattling. But the noise goes away after killing #5 injector, this tells me you could have a problem in the lower end or the injector itself is overfueling causing a "fuel knock" Just curious.
Have you checked your oil level? What Oil do you use? Is it synthetic or base? What weight is it? Cylinder number 5 is the last one to get oil.
Also, there is a test we can perform at a dealership for checking injector leak down (or leak off) while the engine is running. I have seen a couple of cases where injector leak down is fine while cranking.
Also, according to how you've explained the leak down test, not having strong enough battery voltage could give you a false passing test simply because the engine wasn't cranking fast enough in that 15 seconds. Did you have a larger battery charger on it while cranking or at least charge the battery for a while before running the test. It's possible with all of the key on, engine off time messing with this brought the battery charge down too low. But still high enough to start.
Anyway, the engine running injector leak down test is very similar to the cranking test, only the vials are larger and of course you do not disable the engine from starting.