ever since I installed the resistor pack with the peak and hold injectors I've been hearing this light knocking or thumping sound. I pop the hood and listen to the engine but I don't here it, I can mostly hear it when I'm in the car, then I put my hand on the fuel line 9one going to the fuel rail) and I feel the line pulsating at the same speed as the sound that I hear, does anyone know whats causing this? Car idles smooth by the way