Royal Enfield — metal noise from engine

Address:

Chennai, Tamil Nadu, 600107

I have purchased royal enfield thunderbird 350x in september end. After 1st service i have problem in engine noise. I am hearing metal noise once engine got heat i hearing heavy noise. Now i have crossed 7000 km. But from service center they trying to convince me this is the engine sound. They have sent a mail certified that the engine sound is normal.
They was measuring noise by decimal meters. Meter will shows the noise lavel only. It will naver define type of sounds. But they working based on decimal metres.