Yes, on this one, the stationary field is permanently attached to the truck frame. It is similar to the MPC GP 7/9, which was in turn derived from the motor used in the postwar 200 series Alcos and the 600 series switchers.
To service, remove the brush plate. If you are lucky, there will be enough slack in the wiring to do this without having to desolder anything. Then the armature can be pulled out through the top of the motor (may need to give it a little twist as you pull). The bottom of the armature is contained in a sort of pocket in the truck frame: make sure that has some grease in it and is not worn out of round. The top is contained by the brush plate. Grease this very sparingly, lest warm lubricant run down onto the commutator during operation. Note that there is a set screw in the brush plate. Adjust this to prevent excessive vertical play in the armature (it takes a 0.050" or 3/64" hex wrench). The set screw seems also to help keep the upper end of the armature centered.
If the ends of the transverse shaft which holds the worm gear are running dry, this might also be a source of noise.