A xylophone is, of course, only made of wood bars.  Any such
percussion instrument with metal bars is most often known as orchestra
bells or Glockenspiel (German for "bells play").  On a theater organ
the orchestra bells play at a 2' pitch, as does the Xylophone.  The
much lower pitch metal bar sound is called Chrysoglott.

The marimba is a wooden bar.  You will notice that it is a much wider
and larger scale than a xylophone.  The tuning of the xylophone bar is
done by filing the ends to make the bar shorter (sharper).  There is
usually a slight filing under the middle, as that tunes the first
partial in the overtone series.

The marimba has a very deep cutaway under the center of the bar.
This is because to get the haunting, hollow tone of a marimba, the deep
cutaway actually tunes the first partial (normally one octave above the
fundamental pitch) to a pitch an octave below the fundamental pitch.
I know of no other instrument in which one may tune the partials far
away from where they normally fall.

I have never seen a marimba with buzzers or kazoo ends on the
resonators.  I have worked on several and they all have solid soldered
ends.  The resonator is actually tuned to the pitch of the bar under
which it hangs.  If you remove the resonators the volume of tone
shrinks greatly.  I think the buzzers to which you refer are perhaps
found on an ethnic marimba which comes from a limited nation or locale
in Africa.

D.L. Bullock
St. Louis
http://www.thepianoworld.com/