I would wonder if one wheel engaged and the other didn't. That could cause interesting noises. The transfer case is pretty stout.

As for shifting it into gear at 55mph... I've done that for years. I've done it in Bronco IIs, Rangers, and now an F-150. The transfer case design has been the same for 20+ years across both sizes of truck. It works as advertised. I wouldn't worry about it.

I'm pretty sure the 55mph is just to cover their butt too. IE, you shouldn't be going that fast if you need 4wd. But I don't see anything in the case design that makes 55mph a top speed for shifting it. The magnetic clutch really only cares that both driveshafts are traveling at the same speed.

 

Yup, put in and out of 4X4 tonight many times to be sure and the sound is gone. Thank christ, I didn't need another project!!