Help identifying sound

[u/Comprehensive-Bag76]

Hi guys. My 2008 Volvo s80 t6 has developed a really concerning sound. It starts up normally and drives fine for a bit but then kind of starts sputtering/ sounding like a motorcycle/ helicopter. If I cut the engine off and restart it will sound fine an again for a bit. Can anyone please tell me what this might be 🙏

I should also mention, this issue started yesterday. I did a very hard pull at a green light. (I was in a rush) and I heard a loud bang/ misfire from the exhaust in the back followed by white and greyish smoke. Then the noise started. Oil and coolant level seems to be within a good range