Roaring Droning Noise - Exhaust Manifold?
 

I've got a 96' Cherokee with the 4.0L 4x4, 136k miles. At 75+ mph I have a loud roaring droning noise, sounds like bass as if I have a subwoofer playing constant bass. It did it on the old tires and the new ones, has for 1 1/2 years. It doesn't change when tires are rotated or balanced. My Dana 35 had a bad bearing and I swapped in another Dana 35 and it still makes the same roaring sound. It has new U joints on the rear driveshaft as well. I'm wondering if it could be a motor mount (which they don't look that great) or perhaps the exhaust manifold. I have just noticed a crack in the exhaust manifold where it goes from 2 pipes into 1.

Any ideas guys? Thanks.

http://i58.tinypic.com/6sqrmc.jpg

Bump

Does it sound like it's coming from the front or rear?

HHmmm, pushing a unit as aerodynamic as a brick @75mph will make lots of noises.

Just have to look for things not right, especially exhaust rubbing, or maybe you have a poopy muffler.