Echo Alex’s appreciation of the simpler side of things in a Vanagon. 

I, too, have been embarrassed by the noisy side door in a quiet campground in the morning but found that removing the cover and then lubricating all the bearings/sliders (after cleaning the surfaces) really helps a lot. The lower track in particular attracts gravel and becomes a long “rumble strip” of its own.

A bearing kit (with all the bearings and sliders) is available from the usual suspects if you have a “rumbly” bearing that doesn’t improve with lubrication/cleaning.

The other major fix - which I have seen/heard but not done yet - is to remove the inner cover and put some sound deadener in there. I believe the newest (90/91?) vans have some sound insulation in there, but the rest of us have a resonator that amplifies every little imperfection on the slider track and bearings.