Grabbing on front end of 1998 Explorer

After driving for awhile and stopping then start driving again it soundsand
feels like the 4WD is engaging on the front wheels. Is this the result of a
need for a fluid top off?

I was just able to check the fluid in the transfer case and it is really
dark brown. Is this the problem with the grabbing you think? I know I need
it changed BAD so please don't call me stupid..lol... I bought this truck
used and have had it for about two years.

Just got through changing the transfer case fluid with a mercon type tranny
fluid. I drove it around and did some figure 8's in a parking lot that had
shell in it and engaged the 4wd. Ran back on to pavement in Auto 4 wheel
and my problem seems to have disappeared. I am going to drive it about 40
miles in stop and go tarffic in Chicago and see if the problem re-occurs.
I will let anyone reading this as to my findings. In the meantime if
anyone has any suggestions on what to look for please let me know! Thanks!