I know the type of noise you are referring to, it will come on then stop all in a few seconds. I have always thought that to be injector knock as well.

When the injector knock came in my car, out of nowhere, even after a 200 mile trip and I got on it real hard, the knock still did not go away.. it came and went as it pleased and no amount of hard driving would take it away. Before anything, I would try a bottle of Redline diesel additive. Used it many times in that car.