2000 SD SC 5.4 4x4:

While accelerating normally (not gunning it), and I hit 45MPH, the tranny kind of groans after going into OD, and that sets off a resonant vibration somewhere in the front end. If I keep at the same speed I can make it hang around for a few secoinds before it goes away. It seems to be related to cold weather. The colder it is, the louder it gets. It doesn't happen in the warm weather. It's worse when going up an incline.

It sounds like it's coming from the drivers side behind the dash. It's sort of a rattling vibration.

I know it's a long shot that someone else has had this same sound, but it's worth a shot.

Thanks.

 

Is the front drivetrain spinning? You may have a hub stuck (or locked) or the t-case stuck in 4x4.