That sounds really frustrating! New electric vehicles can sometimes have a few issues, but a chugging or train-like sound is definitely odd. It could be something like the braking system, bearings, or wheel imbalance causing the noise. It’d be awesome if you could share what the issue ended up...
It's on the Kia site. Try checking these out.
https://kiastuff.com/2019-2022-kia-niro-ev-weathertech-cargo-liner-m032/
https://kiastuff.com/kia-niro-cargo-mat-with-seat-back-protector-m021/