My car has started 'pinking'. ( An almost inaudible tinkeling from the engine) That's what it sounds like anyway. In the 'olden days' one got it thro' pre ignition. Modern cars ignition is computer controlled so I am at a loss. It orrurs in high gear, low speed, less than 30mph, with a slight pressure on the gas, it stops when the peddle is raised. Garage says not to worry (?) but didn't identify the cause. I've changed from supermarket petrol to Shell, it's still there. Nothing's been done to the engine and all is as it ever was. Any ideas?