BX23 loud hum in 4wd then pops out back in to 2wd

[Roverguyjoe]

My bx has developed an issue with 4wd. When it’s engaged it makes like a low humming noise and then eventually pops out of 4wd back in to 2wd all on its own.

Did some searching on the forum and found some people discussing an adjustment for the popping out of 4wd issue but nothing about a mechanical, humming noise prior to it.

Any suggestions before I just blinding start digging into it?

The noise sounds expensive and I’m a little worried…..

 

[North Idaho Wolfman]

It could be as simple as it not fully engaging causing it to hum as it's only on the edge of the gears.