I was testing out the ABS on my 99 runner and when I would slide on some ice I heard a grinding noise. I am used to ABS making a thumping noise. Is this normal for the ABS to sound like this on a 4runner?

 

From what I have found by searching, its normal for the ABS to make a hideous noise when it triggers.

 

Yes unfortunately YES. It will cause the brake to feel like it's pulsing (which it's designed to do) and the grinding noise you are hearing is from the process of the ABS. I'm too lazy to look in my auto tech books but there are 4 different things for the ABS to do to prevent lockup (I may be wrong on Toyotas but according to my GM training books there are 4 different things the ABS does).
I will go ahead and warn you that it will do that on potholes and trying to stop suddenly... I had a bad near mishap from that when a yellow light was on and the car in front of me slammed on the brakes and as did I but right when I hit a pothole. The ABS did the same thing and I nearly rearended the person.