So over the course of the last few months there's been this super intermittent knock that comes about. Only under load, so far. Even then I can't reproduce it. Typically when going up hills. Increases in volume when I apply the pressure on the gas pedal. But whats tricky is that I can't find the right circumstances that reproduces the sound... I could really use some help on this. Ideas? Rods? Lifters? Loose pulley?