A whine is usually associated with a clog or pump failing. Unfortunately there's nothing serviceable besides the fluid, so I would do a series of changes several hundred miles apart until you get a red'ish fluid and if it hasn't helped it any then try a flush a fill. That may be your only option besides a repair/rebuild job which is probably more than the vans worth. But if everything else is in good shape, maybe it's a cheaper option then buying new/another used.
Last edited by Mad_Hatter; 02/21/20 12:57 AM.