2007 Bajaj Platina "high pitched sound driving stops" Questions

...high pitched sound as if decompressor is working and I had to throttle down and bring the speed down to 20 to 30 kmph for a while and the sound stops. Again I can throttle up to 60 but after a while ...

high pitch, very loud. If I stop and start out in 1st gear the sound most times gos away. If I start out in second after the sound starts, the sound is still there. This sound doesn't happen everytime