sweetyankee proclaimed:

   The serpentine itself could be old and squeaking.  You can carefully
   run a bar of cheap hand soap along a bit of the belt and see if that
   helps, then wash it off later.

   If you have a bearing squeaking, get a long thin tube and drop a bit
   of heavy motor oil into the bearing.  A piece of electronics
   "spaghetti" from Radio Shack works.  I've seen this work well enough
   to put off repair for a few months.

The harmonic balancer part of the crank pulley breaks(rubber fails). New
or used will fix it.