Dear I am also facing the same issue in my bike but there is no vibration in my engine. I purchase yb 125z on 19march 2019 in my bike there is engine noise issue. I have don 1200 km on it. But from very first day i feel unwanted sounds, like timing chain nose and some other sound as well. On first oil change on 500km i bring this bike to 3s dealer, but their mechanic said to me noise is no issue, if feel some performance issue then only you can complain. I am so disappointed, but i will raise this issue again on my 2nd service.
One more thing, this noise is negligible when bike starts in the morning, but when engine reached to its normal temperature noise also increased.