Sportsman 550 XP bang and turn off

Hi all,
this afternoon i was doing a tour with my Sportsman 550 XP while I started to hear a strange noise like a creaking/chirping.
At first i thought it was the belt and i went back but after some minutes i noticed that the quad bang when i release the accelerator and i struggle to engage the gears H/L/N/P. Stopping I noticed that the quad goes off if I left it in high gear and with brakes on.
Now the quad turns on, it remains for a few seconds accelerated and then he brutally turn off.
I can not understand what it it might be. Can you help me?
Sorry for my english