1999 Mazda Protege mileage: 18,000. 1999 Mazda Protege 1.6L, 18000KM. Just had 16000KM service done and asked them (service guys) to look into an Acceleration Rattle. Since then they have checked the heat shields, replaced the Catalytic Converter and the Catalyst. It is only during acceleration (at any speed). Sounds like marbles bouncing around or pinging. Any additional ideas that I could have them look into?