I also have been hearing a pulsing noise at speed. Sounds sort of like:
...vwah vwah vwah vwah vwah vwah... ?
anyway in the process of tracking down an intermitant power loss problem I read that the fuel accumulator reduces pulsation noise of the fuel pump.

Let you know if anything develops further.

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html