Sounds like axle wrap to me, but I've never heard of it on a 4Runner, but it's a well known fact that Taco are notorious for it. I've heard that one way to cure this is to squirt some new grease into the different points in the drive shaft, u-joint, etc. Here's a link from the maintenance section:

http://www.4x4wire.com/toyota/maintenance/tacoma_4runner_30k/maintenancep4.html#driveshaft

Maybe that will help.