When I do a cold start, there is a 1 sec rattle. When I drive off, whenever the rpm crosses the ~1500rpm mark, there is a rattle sound. Only at that particular rpm. After 15mins of warm up, the rattle disappears completely! Is that piston slap? Im using SPC 0w30 oil. What should I do? Use a heavier viscosity oil? Get it scanned for any trouble codes? The CEL didnt light up though. It only has 20,000km on it.