Around the 3,000 mile mark, my Bolt started making a "metal hitting against metal" sound from under the rear of the car when the weight of the car shifted from left to right and vice-versa, such as when going around corners. It wasn't very loud, but imagine a sound similar to hitting a metal pipe with a small tack hammer in the distance.
The ride didn't seem affected to me, but I eventually took it in to the dealer, who after much effort diagnosed it as something like this explanation:
The rear axle is made of a strong bent tube (a torsion beam suspension), and a metal piece from the wheel fits into that tube and is welded in place. The weld has somehow broken, and the metal part is moving slightly inside the axle tube as it flexes, resulting in the noise.
They said it's not a safety issue because the metal part is long and can't come out of the tube, but it should be fixed to stop the noise and possibly improve the ride a little.
I didn't hit anything, etc., and the dealer said that the original weld was probably defective. In fact, they said GM is aware of this and published a service bulletin suggesting that dealers fix this by drilling a hole through the two parts and riveting them together... but the service bulletin has since been withdrawn for some reason. Instead, they ordered a new rear axle bar, which took a couple of weeks to arrive. The car is in the shop today getting it replaced under warranty.
If you hear such a noise, well, now you know!