You don't say where you're located, but here in the northeast, when the temperature goes down, the knocking complaints go up! Every year around this time, the "knocking when cold" complaints start to trickle in. Carbon build-up is by far the most common cause for this problem. Try some Techron fuel treatment. I'll probably go through a dozen or so cases of it before the winter's over. You'll probably have to treat two or three tanks of gas before the noise goes away completely.


P.S. The Air Injection Pump is known for making a high-pitched whining noise immediately following a cold start. If you still suspect that it's the cause of the knocking noise you can simply disconnect it before you start the engine. If the noise is still there, it's not the pump.