it is common fault of cg125 chain cover, some kir kir occurs on bad roads. Recommended free play is 20mm and its not much so set correctly and make sure indication marks are aligned see the user manual. mostly i have seen atlas bikes comes with accurate chain settings from factory its the mechanic that don't follow guidelines for company recommended settings. If you are unable to resolve issue you visit mechanic.
however i suggest kir kir from chain cover in common in all cg 's. if its same sound just ignore if its too much than visit mechanic and ask him to check