I certainly am not an expert on this subject, but I'll throw in a
couple of other items that I've read about related to this symptom:

  - Is the oil too full?  Should be between the add and full marks,
    absolutely not OVER the full mark at ALL.  Ideally about midway.
    Do NOT add oil unless it is UNDER the low mark.

  - Is the oil correct?  Unless you are in very cold climes you want
    20W-50 or so, even in the winter consider Mobil 1 15W-50 it will
    still flow well at well below freezing temps.  If you're in Alaska
    or parts north, you might want a lighter oil in the winter.

  - Consider installing an oil pressure GAUGE so you know what's
    really going on.  Idiot lights/buzzers are great for calling your
    attention to a potentially critical issue, but don't give you many
    clues beyond that.

My $0.02.

Allan
--
1991 Vanagon GL