The arm that slides the locking collar in place is held under tension by a spring until the gears line up and the collar can slide in to position. The sound you are hearing is the spring forcing the ring on. It's normal.
When you press the button, that just actuates the locker.
It won't actually engage and lock the axle until the 2 halves are lined up properly. If you hit the button, and drove straight and steady on even ground it might never lock. But usually if you press the button, and then drive forward and turn one way or the other, or let one of your wheels slip, it will line up and engage faster.
It's the same when you disengage the locker. It won't actually unlock until it's aligned properly, and the little mechanism can retract.
Anybody living in the Northern salt spreading states should be sure to clean their actuator thoroughly.There is a small pocket between the actuator and the rear housing. Salt, mud, and other debris can get in there and rot the housing of the motor. It's easy to change but the new actuator is $800. Luckily I found a guy on TTORA that had a spare for $200. It's also a good idea to engage your E-locker on a regular basis. i.e. monthly/weekly. Sometimes the gear inside the rear sticks from inactivity. Sorry to ramble.
I have experienced this same thing with my '01. Thank you for asking this. I'm curious to see what other responses might come up.
And due to the vagueness of your title, I'm going to use this chance to politely [albeit, slightly] hijack while we have a captive audience...
Why does my e-locker make a popping sound when it disengages? It's nothing "scary" loud, but there is a slight metallic ping to it. Anyone else experienced this?
(Seriously, my apologies for tagging along another question, Rthario.)
No worries, hope the responses to your question help.