ML fuel pumps don't "buzz".
If you are hearing a noise from your
left rear wheel well it is probably
the fuel pressure regulator which is
located in the fuel filter. If you didn't have to
change the lines also then you installed a
old style filter. Do your self a favor and
get the new style with updated lines and install
it or just live with the noise. Sometimes it'll go away.
If You bought the filter from a dealer have them
parts warrenty it. Should be N/C to you to
replace I believe.

Emmett.