Grinding or clunking during four-wheel-drive operation may involve the transfer case, axle engagement components, joints, or other drivetrain parts. The selected mode and whether the shift completed are important details.
Some vehicles make a brief engagement sound during normal operation, but repeated grinding, a new heavy clunk, or noise accompanied by vibration should not be dismissed.
Do not keep cycling the selector to reproduce the noise. Contact Certified Transmission in Council Bluffs for an inspection. If the vehicle binds or the noise is severe, stop driving and arrange assistance.