i just noticed this yesterday...
i was in 4low, and turning in reverse and i heard a clicking, kind of a "klunk" sound. it reminded me of the sound when i broke a cv axle but it wasn't as loud. so i got out, checked things out and noticed a bunch of grease around the passenger side inner cv boot. not sure how long it had been there but that's when i first noticed it. i cleand it up and ther doesn't seeem to be much more new grease today . a little new grease i think, but not much.

i wanted to test things again today, and everything seems fine in 4hi and 4low going forward...but when in 4low reversing, specifically when turning i hear that low pitch clicking kinda sound. can't tell which side it's coming from. and it's only about once every wheel turn. so...what's up?

 

Hell if I know, here's a bump though.

 

its your CVs binding. 2.5" lift + 4LO + turning (forward or reverse) = binding.

the turning probably stretched your boot a bit causing some grease to spew out.