growls like it's on mudders

My 2004 RAM 2500 4x4 all at once started growling like it's on super mudder tires. It does it over 45 mph or so and continues even if I slip the trans to nuetral. 1st started only on deceleration, like from highway speed to stop sign. Is it rear gears? It is limited-slip. I do pull a small open car trailer with a A body several times each year and truck has 94,000 miles on it now.
Thanks for your thoughs, fix ideas welcome also.

the late model limited slip 9 1/4s have had problems with the the clips that hold the clutch pack together and can work loose causing damage to the rear. Have it checked.

u joint maybe