2002 Peugeot 206 Jumping Out of 1st Gear and Clunking Noise

My Peugeot 206 has started to make a tinny/clunking noise underneath it when setting off in first gear when the engine is still warming up. It doesn't seem to do it once into a journey, just when the engine is still a bit cold. I have only noticed this since I had a new exhaust fitted a couple of months ago - not sure if this is related.

On 2 occasions in the last few weeks, when setting off in 1st gear in slow traffic the gearstick has jumped out as well, back into neutral without stalling the engine. Both times it happened it seemed to jolt quite heavily.

Any ideas what the problem could be?

Thanks