Bad News Guys....

Little bit of backstory:
I have a 2002 4runner with 150k miles with a few mods and bigger tires but nothing too serious. A couple days ago I drove through some rarely found mud pits in the desert, and everything seemed fine and dandy. Last night driving home from work I noticed a circular squeaking noise coming from right underneath the driver side door/seat. I had a couple friends try and pinpoint the noise and it sounds like the driveshaft or transfer case, and the noise is strongest at 1200rpm.


Symptoms:
-Strongest at just above idle
-Seems to be below the driver side door panel
-High squeal below the car, sounds in a circular series
-Disappears at 2000rpm
-Any Gear has the same symptoms
-Not a locking rear diff
-Drives fine still

Now I'm hoping with all my heart this could just be a lubrication issue that the mud made, but could it be something more serious?
Tonight i'm going to jack up the rear wheels and idle the car in drive staying still so i can pinpoint the sound.

Any help is appreciated!
Thanks guys.