Pinking is easy to hear if you don't have a stupidly loud exhaust or stereo.

It sounds like a rock rattling around in the engine. Its also called 'Detonation, Knocking or pre-ignition'

Speaking from experience it can be *very* harmful to your engine so if its doing it get it checked out ASAP.

Late model electronic ignition cars usually have a "knock sensor" that detects knock and adjusts spark timing to eliminate it, hence another reason why higher octane fuels should be used in engines. Higher octane fuel is less prone to pinking so the ecu can keep the timing where it should be, creating the most power not all over the place trying to stop knocking.

One of my old V8 Fords pinks quite bad on regular or poor quality fuel, but runs perfect on premium unleaded. Fuel does make a big difference for pinking. But if your late model "computer controlled" engine is still pinking on good quality fuel, I would be getting it to a mechanic quick-smart.