I want to ask why the engine of Komatsu excavator has abnormal noise.

The exhaust manifold gasket may be damaged. Check whether there is blackening around the exhaust port. If yes, replace the gasket. This happened to me last time, and the sound was like the sound of a broken exhaust pipe. Then I went to an excavator repair shop, which seems to be called Guoxiang excavator repair shop. If your situation is particularly serious, you can search for it and try to fix it as soon as possible!