A Dutch article about this [1] said:

> According to the Chinese space agency CNSA, the sounds are caused by the interaction of different metal parts.

In the video, they also quote the person leading the Mars programme:

> The sound is made by wheels rotating on the surface of the Mars rover. Basically, the sound of different metal objects bumping into each other.

[1] https://nos.nl/artikel/2386872-chinese-marsrover-stuurt-nieu...