[bigcoconut]

It sounds like your van has the towing package with the air suspension on the rear axle. My air pump makes the same noise just after starting in the morning and other times when the suspension needs leveling.

The noise is simply the small compressor located at the rear just under the body on the drivers side. If you have the air suspension than you should have the air valve for accessories (blow up pool toys and soccer balls, that's what I use it for) in the back behind the last row of seats on the drivers side wall.

As long as the van body remains level from rear to front than you are OK. Basically the distance between the top of the tire and edge of the wheel well on the body should be about the same on the front and back. The noise is 'normal' since air pumps/compressors are never really quiet.

Hope this helps...