Center differential light flashes when reved up in neutral

[Oregonian]

Basically I just bought my 2001 4runner SR5 and I had some rattling coming from the muffler, when I was revving it up to show the guy at the muffler shop ( to about 5,000 rpm ) I noticed the center diff light was flashing orange ( in neutral and 4x4 off ) why would that be you think? Thanks everyone, new to 4x4 just sold my 02 prerunner and picked up the 4runner