1. If the engine middle part is making and irregular "ka tak" noise when it is idling, the noise soften or become disorderly after increasing the engine RPM and conpletely gone in high RPM range, it might be due to engine hydraulic lifter malfunction, suggest to proceed to workshop for diagnose.
2. The common issues of engine hydraulic lifter making noise are: engine oil pressure too low or too high, causing engine oil with bubbles go into the hydraulic lifter forms a elastomer which produce noise. Engine oil pressure too low and lack of lubricant oil in the hydraulic lifter, causing air go into it and produce noise. Engine left unuse for a long period, causing the hydraulic lifter being over compressed, after restarting and there is no sufficinet engine oil hence air go into it and produce noise. Hydraulic lifter failure, produce noise.
3. For your safety, suggest to diagnose at workshop as soon as possible, if the condition is sever, suggest the owner to call for roadside assist to avoide permanent damage to the engine
Suggest to perform diagnose at work shop, usually the keypoints of diagnose are:
1. Open up the engine, check the plunger wear condition.
2. Check if there is oil leak at the valve.
3. Check if sufficient engine oil pressure is supply to the hydraulic lifter.
4. Check if the plunger and lifter are clogged by the oil contaminants.
5. Replace the parts with heavy wear sign or leakage, repair the parts with minor wear to continue using.