piratetim

I am getting a very light knocking/tapping noise. It will only happen when the motor is very cold and the temperature is very cold out and I first start the car. It will knock for a second then be perfect. I also notice it when im about 4k-4500 rpms and I let off the throttle so that there is almost 0 load on the car. The 3 rd area I hear it is sometimes when I let off to shift. And its never for long just a split second. Is the oil pump's pressure directly correlated to whether or not the motor is accelerating? It seems like the oil isn't getting somewhere in the motor just for a split second when I let off the gas. Any ideas?