A sharp sound was coming from left side of engine (like ghoon ghoon). It started coming from the very first day when i took it for a long ride of 50 kms and drove it upto 70 km/h (kept RPM below 6000 as prescribed in Owner's manual)
Yesterday I reset its timing chain tensioner myself, the sound significantly reduced. Today took it to dealership for first tuning. The guy there told me to bring it back when there is almost 1000 km on odometer (the bike has done only 640 km). I asked him to change its engine oil since I need to take it out of the city although first oil should also be changed when bike has done 1000 km. Regarding noises coming out of engine he said these will go away after first tuning.
So people who hear odd noises coming out of brand new YBZ or YBR, just bear them till first tuning. Usually these noises are produced by tappets or timing chain. And even after first tuning if you still hear minor noises, just get used to them and don't destroy its engine by opening and changing things.
Plus I would ask people to stop listening to stupid mechanics who would tell you to change first oil at 500 KMs and keep speed below 50 km/h. Do they know more than the company who manufactured whole bike from scratch? You could take bike to 6000 RPM regardless of speed but don't drive it at fixed speed. Keep increasing and decreasing speed until you complete its break-in period.
Read owner's manual and follow that. Company didn't provide you that to toss that away after purchasing vehicle.