That is what it sounds like to me, especially if the sound is coming from the diff housing, which is not good. But, I would make sure that is where the sound is really coming from before I tear anything apart. Keep hope alive.....maybe it's something not so bad.

I crawled up underneath it and the drive shaft is tight! No play what so ever! What next? I guess I will try to jack this thing up!

I'd bet for sure it's carrier diff bearings.

This is very common on higher mileage Toyotas that haven't had the diff oil changed on a regular basis. If you're hearing a howling sound from the rear diff, that's very likely it, IMO.

Drain the diff fluid. It's probably pretty mucky or at least silvery and stinks like heck.

If I remember correctly, mine only made the noise under a load. When I let off the gas, it went away. When I finally pulled out the old diff and took apart after replacing it with a new unit, the carrier bearings fell apart in my hands.

Now that you checked the driveline, next thing is drain the diff fluid and examine it.

*update* The problem is the diff., I drained the oil and it was totally silver. After putting new oil in, it did quiten down a little. BTW, what causes the oil to turn silver? Is it shavings over time?

my 86 4runner did the exact same thing- let me guess- whooooooooooooooooooo...... until you let off the gas right?
on mine it was the pinion shaft bearing. it was a result of using oversized shackles (to cure the saggy rearend).