I am getting a consistant knocking noise coming from the engine. It is loudest at lower speed/revs. It does speed up when I go faster, but doesn't slow down when I change up a gear. Its more of a knocking than a tapping. I can't hear it at 80KPH+, but that could be duw to wond noise. Any ideas what it could be? I am leaving it in for a full service this weekend but I want to know a few things that I could say to the mechanics so that I don't sound like a muppet. From what I understand, it could be sparks, fuel or compression. The fact the rate of noise doesn't change when gears are changed, would that rule out compression? Any other ideas as to what it might be?