Need help on part .

[npsambi]

I have been having a rubbing noise in the left rear of the Tahoe mostly heard around 40-50mph. I thought it was the brakes but changed those out(needed a brake job anyway) and noise still exists. I thought it was the axle bearing so I pulled the axle today and in the process of pulling the bearing I busted this star looking piece of plastic which looks like it holds this sleeve inside the axle tube. I'm not sure why that sleeve is even in there?? The axle has a bearing on the inside and on the outside so why would it need this sleeve at all? Any ideas or reasoning why this sleeve is there and what it's purpose is for? Thanks

Info on Tahoe:
2007 71k miles 4wd 5.3l

Here are the pics i took:
THe star piece I busted made out of plastic:
http://i2.photobucket.com/albums/y10/npsambi/cehvyrearaxle2.jpg

Slides in front of this piece before the bearing goes in:
http://i2.photobucket.com/albums/y10/npsambi/cehvyrearaxle4.jpg

Thanks for any info on this. Seems to also be a dealer part that I will have to get tomorrow.