Today I took my 4-cylinder, 5-speed TJ to an off-road trail in Colorado. Everything was going well for a while, and then it happened. Going downhill in first gear there came this ugly noise from underneath, as if the gearbox were chewing rocks. Then I came to a complete stop and the noise persisted for a few more seconds and then went away. That happened several times. When I got back on the pavement, no problems. Based on my description, do y’all have any inkling what the problem could be? This happened in 2H, 4H, and 4L. Thanks.