Pinking is usually caused by detonation, rather than pre-ignition. People often confuse the two things, but they are actually different and caused by slightly different things.
Pre-ignition, as nathwarr says, is caused by a red-hot bit of carbon or perhaps an overheated spark plug which causes the fuel mixture to ignite before the spark.
Detonation is different. If the mixture is wrong, or if the charge pressure is too high (even on a normally aspirated engine - like when you've got your foot flat down in top gear), then the mixture can "explode" rather than "burn". In a normal combustion event, the flame front should move smoothly across the combustion chamber, spreading out gradually from the spark plug. The cylinder pressure should rise smoothly and gradually, only reaching its peak when the piston is already on its way back down. During detonation, you get pockets of mixture that explode suddenly, so you don't get a nice gradual burn and the combustion pressure rises far too quickly. But the key thing is that detonation occurs after the spark has ignited the mixture.
The "pinging" noise in detonation is caused by a shock wave that bounces off the cylinder walls, setting up a standing wave. In smaller engines the frequency of this wave is audible as a "tinkly" noise, but in big engines the sound is lower (because the cylinders are bigger) and tends to get drowned out by the rest of the engine noise.
Light detonation is nothing to worry unduly about - in fact many engines are intended to run with a little bit of detonation. If it gets bad then it can lead to overheating, but is unlikely to damage the engine quickly (though it's worth getting it sorted if it's bad enough to hear it). Pre-ignition, on the other hand, is always BAD. Your engine will die very rapidly. The fact that your engine is still running means that you don't have pre-ignition.
![[B)]](/forums/styles/seatcupra/oldforumsmileys/shades.gif "Cool [B)]")
