Is it second hand or new ?
If it's new, return it to the seller.
It certainly sounds like the gears are grinding.
Have you run it in ?
If it was mine I wouldn't be running it ?
You can unclip the bottom bogie covers on each end with a small blade or flat screwdriver, be very carefull not to snap them.
The cover should come away leaving the wheel sets exposed.
If you need to drop the bogies out, you need to remove the body by taking out the four screws underneath the chassis, a long small cross head is required, once the body is off you'll need to drop the bogies,
But first unfurl the wires going into the holes to give them some slack to allow the bogies to drop.
Good luck.