Royal Enfield — engine over sound

Address:

Palakkad, Kerala, 678582

After running 40 kilometer a big sound from engine room. I was all ready show the complaint in my near showroom but they are not identify the problem. So what can i do next and how to close the problem. I have royal enfield classic 350 gunmetal gray.
I need the detaild explanation about my problem immedietly
My contact number: [protected], [protected]