the break in oil was prob a conventional and heavier. the synthetic is prob thinner and has made the noise audible. when i first drove my car with the locker it freaked me out but i dont even notice it any more and i have thousands of miles on it.
X2
I have noticed Dana 60's sounding noisier when changing from a thick oil to a thin oil (synthetic). Higher static viscosity's have insulating properties. just like if you use a paint stir in a drill, you will get two different noises between mixing water and mixing laytex paint.