Really Bad Rear End Noise

[havok88]

So I had some yukon 4.10s installed a few weeks ago. When I picked up the truck from the shop and drove home I was real gentle on the gas, let it cool like I needed to and all. But had an ever so slight whine when decelerating. I have heard from some people that a little whine is normal. But when I called the mechanic this morning he said it is not. I am over the 500 mile period when the diff fluid needs to be changed because I have not been able to get back to the shop since it is a long ways from my house, but was planning to get it in tomorrow. Well I was driving to work this morning, and when I pulled up to the gate, I get down to about 30mph and it sounds like a 2 stroke dirt bike coming from my rear end. anyone know what this is? The truck will be going into the shop tomorrow to get looked at. just wondering what I might expect to hear. from reading around it sounds like a bad pinion bearing or the pinion preload loosened? not really sure what that means or what is involved in fixing this. what are your guys thoughts?

 

i left the truck at work tonight that way it will be a shorter distance to the shop in case anything is really ****ed up.