Hi guys , a new problem in my Pulsar now. After engine rebuild of my Pulsar, my Mech asked me to not to exceed 50 kmph till first 1000kms, so I didn't exceed the speed of 50 kmph. But after riding continuously for like 30mins or 1hr maintaining speed of 43 to 47, a hissing sound also joins and after one hour the sound changes too loud like something is crushing inside engine. After giving rest to bike for more than 4 hrs its again back to normal.

What's this problem? Any info on this problem will be useful...