Noise from the rear when turning in parking lot

My 2006 TRD Sport, which as the limited slip rear end is making a, I guess I would describe it as a howling noise when I turn in a parking lot. I added the limited slip friction modifier when I changed the rear end oil last time. It's only been about 15,000 miles, give or take a few. Should I add some more, change it out again, or could this be something else?

 

What oil did you use last time ?
I vote for changing again. When my oil gets old I get the same thing so I just change it and its all good.