is it normal for a 940 non turbo to knock when using low or mid-octane fuel? my car seems to do this, especially when I'm only accelerating very lightly. I'm at sea level and the temperature is in the 60s, not too humid. It's recently had a tune up with new plugs, wires, rotor/cap, oil, fuel filter, etc. the engine seems to run strong other than this knocking, but it is quite noticeable. is it possible that there would be another sound that sounds similar to knocking that I'm mistaking this for? It certainly doesn't make it when I rev the engine in neutral, under no load. but it also doesn't do it under heavy acceleration, which is when my old 122s would knock, and with less sound insulation on that car it was much easier to distinguish the sound.