2011 Toyota Tacoma rattling noise from rear

Hi there,

I have a 2011 Tacoma automatic, 125K miles had it in for 100,000 mile maintenance. Since then or course of last year I've had a humming sound driving at lower speeds while in gear, put it in neutral and quiet.

Now just recently I am getting a rattling sound which happens at lower speed on acceleration and then goes away at higher RPM or speeds.

Dealership couldn't get me in today so I took it to Firestone, they couldn't pin point the issue but suggested that it's possible pinion bearing or some type of differential issue. They suggested taking it to a specialty that deals with drive train. Which I'll probably end up doing, I've read other posting and seen various issues and results. I recorded the noise and uploaded it here if you anyone wants to listen and/or have any ideas of what could be the possible issue and what to expect for costs?

http://vocaroo.com/i/s1QY8eGUbsVS


I'm not that mechanically inclined to take this on myself.