Is this noise normal when in 4WD?

Hey friends, I just purchased a 05 chevy suburban z71 with 56,000 miles. Has the 5.3 vortec. The vehicle looks mint inside and out. I noticed when switching from 2wd to 4hi on the fly there is a humming noise that starts around the front end. Is this normal? Also when in neutral going from 2wd to 4low you can hear a clunking sound when it switches over. I did this several times and it appeared the clunking noise seemed to quite down after a few times doing this. I also noticed that the 4wd symbol is not lighting up on the dash as the manual states it would (possibly fuse). It clearly kicks into 4wd though. I don't think the 4wd has been used very much in the vehicle. Could non-use be causing this? Maybe just low on grease? I have 30 days to return if there is a problem so any answers would be greatly appreciated.
Thanks

Hey friends, I just purchased a 05 chevy suburban z71 with 56,000 miles. Has the 5.3 vortec. The vehicle looks mint inside and out. I noticed when switching from 2wd to 4hi on the fly there is a humming noise that starts around the front end. Is this normal? Also when in neutral going from 2wd to 4low you can hear a clunking sound when it switches over. I did this several times and it appeared the clunking noise seemed to quite down after a few times doing this. I also noticed that the 4wd symbol is not lighting up on the dash as the manual states it would (possibly fuse). It clearly kicks into 4wd though. I don't think the 4wd has been used very much in the vehicle. Could non-use be causing this? Maybe just low on grease? I have 30 days to return if there is a problem so any answers would be greatly appreciated.
Thanks

this all appears normal...do not operate the vehicle in 4WD/AUTO 4WD on solid DRY pavement..the vehicle must also have tires of the same size with the same wear...when in 4WD all the wheels are locked together,,any difference in tire size will rapidly wear out this drive train...[part time] 4WD...

engaging the 4WD to test for proper operation do so with the vehicle stopped or rolling at a slow speed,,when on solid dry pavement..the longer it takes to engage into 4WD this usually means the transfercase TRACII fluid must be replaced...it is a blue color ...