I love my dime a dozen electric shift BW 1354's.....
I can rebuild the shift actuator to make it work like new, so whats all the hype about having a manual shift (they do have a lsightly lower low range if I remember right, but big whoop)
I can get the electric shift T cases all day long for about $100 here in Denver, last I checked.........
Well if the noise is not there when you are in N then it is definatley a rotating mass in the drivetrain, IE T case, Tranny, or driveshafts.
Get under there and triple check your motor and tranny mounts, check the U joints and the slip yoke on that rear driveshaft real good, triple check the fluid level in the t case, check all your shift linkage under there and make sure its not something stupid like the shift arm hitting the tranny hump or something.........
I know a guy (Brett) is selling a manual shift 1354 right now! (hehehe)
Are you sure you cant get that Atlas II? after 3-4 of these suckers you would paid for it already! (dont worry it will be a long time before I can get the Atlas II I want too....house first, I keep telling myself.........