Verna 2004, Hyundai, when heating he sounds a lot, like noise of divers, new oil?

Hello, Hyundai Verna (Accent) 2004, a tree cams, 12 valves, when the engine is heated, it begins to sound a lot, as hydraulic divers, but it has power, it is economical, it works very well, but it makes a lot of noise, it is added additive remurs and new oil, asks all these models sound? Is any factory defect? Any partner already found the fault? Share, thanks