Yes , you are right. I used to work on them. The wheel motors were huge. If my memory serves, I think they were direct current.

Some haulage trucks have electrical connections like electric trains so that they can travel up long ramps out of the mining pit. Basically they have an overhead rail like trains and that allows them to tap into a power grid. I imagine such a setup could allow for greater running efficiency.

I wouldn’t think electric motors that large would be quiet. There is also the sound of the wheels as they roll and any hydraulics for steering. Good question though.