When I pushed the 4wd button on the side of the 4wd handle instead of it going into 4wd the lights on the dash that represent 4wd (green wheels-yellow differential lock) just flashed on/off 10-20 times and then it finally engaged with a pop noise under the 4runner. I pushed the button again it started to flash again like it was going to turn off but it just kept flashing. I had to stop, put it in park, kill the engine and restart it, it stoped flashing. It did this several more times trying to engage the 4wd. Finally it was going in and out without any flashing lights. But every other time it seems that it would hesisate to engage and there would be a poping sound coming out from under the 4runner.

 

its an 02 w/ only 60k.

 

This happens to me too, probably flashes for about 5 seconds, pops, and then engages. I think it's normal.

This is my first 4Runner, let alone first 4WD so I don't know much about the whole system besides the fact that when 4WD is enabled, all 4 wheels are powered by the engine.