I have an 04 TJ w/ the 4.0 I6 and NV3550 5 spd tranny. I have an occasional, unusual and very loud clunking sound coming from somewhere underneath the jeep and have been unable to pinpoint where exactly the noise is coming from. It only seems to occur under after days of hard driving. This generally involves a significant amount of driving without a lot of rest or after pulling a small 5 x 8 landscape / utility trailer. On a normal day when I only use it for work commute, I do not hear anything out of the ordinary. I first noticed the noise after I moved from one house to another in the same city. I made about 5 trips across town with the trailer loaded with furniture which probably weighed a little over the 2k lb max. Shifting is smooth and I have the normal "marbles in a can" noise in neutral but this noise is more of a grinding / clunking sound that also seems to worsen when I turn the wheel or taking off in 1st gear or the worst when I am attempting both. Any ideas would be greatly appreciated. FYI, mileage is 181k with original motor / tranny. Thanks!