Unusual sound when letting off throttle and accelerating

This is my first bike so I don't know if it is normal but whenever I let off the throttle or when I'm accelerating, the bike's engine sound like its rattling sort of. Idk maybe I'm crazy. You can hear the sound in the video when I'm coming to a stop and also when I shift into 2nd and 3rd gear. I swear the bike never sounded like this. It has a M4 slip-on by the way. Also when the bike is idling, the exhaust sounds "wet" likes there's water in it. And sorry for the wind noise, I don't have a proper mic yet, I'm still using the built in mic.

https://reddit.com/link/1dvmga8/video/nv3txp3qrlad1/player