loss of power pinging

Hi I need help here. Have had my series 1 for the past couple of months now. Was running great until a couple of days ago. No warning symbol and No fault code is shown. It cranks and starts fine and drives fine for a good distance, however after driving for a while (maybe when engine warms up), pressing the gas peddle emits a pinging/rattling noise and the car would lose power. By steadily maintaining the rpm below 2 the pinging noise is not heard. If i stop for even 20 mins. Its fine again until after a while then the pinging starts. This only when car is in motion, when idlin it does not do this. Would anyone advise what this is and what i need to replace? Does it have to do with the fuel delivery system, broken pump or worn filter? Im a bit lost when it comes to engines so would appreciate what i should look forward to when i take it to a shop.