I replaced isolator bushings about a year ago. I heard a "clunk" when shifting from P->R, R->D or P->D, basically when torque was applied the front differential rotated and the inside case smacked against the case/frame/Diff. Sometimes when it downshifted into 2nd it would "clunk" too. I replaced them my self on a full Saturday's work. The front diff bushing was fine but the two rear bushing were completely separated. I never had a howling though. Like THEIFNDNIGHT said, howling is likely something to do with your driveshaft beginning to fail, more than likely from a torn boot at the transfer case. I don't think the angle variation would damage it, unless you already have altered it with a lift kit.
Here is the link to my post.
2007 wk clunk when slowing down...?