Lippert has a section in their slideout manual on this. It is the gearpack that makes the noise. They say to loosen the bolts and use synthetic 10W30 (Mobil-1) to lube the gearpack. Go to their site and click on customer service, click support center and click slideout selections on the left (half way down). Find through frame and click on your slide mechanism (I clicked on electric 2.5 X 2.5). Across the top of the parts diagrams you will see a selection for manuals. Select the through frame electric service manual. On the 2.5 X 2.5 Electric you will find the procedure for lubing the gearpack on page 8.
I have done this and it works. Sorry, I am not computer savvy enough to make a clicky. Perhaps someone can do it for me.