Walt, I don't know what it is, but I had one fuel pump that made more noise, so I replaced it, and that was 2 1/2 years ago, I see no difference in hot or cold. I hear all the post about it, but have never experienced it myself, 110 or 40 degrees, no difference. John Hervey << For John H, Except for the recent screeching sounds, this pump is as noisy as the one that came with the car. So I suspect that the problem isn't the pump and more than likely just hot fuel for whatever reason. You live in a hotter climate than I do, so have you noticed noisy pumps with hot fuel? >>