back pressure!
 

it is a 190e car

when i open the gas tank cap,i get a rush of air from the the gas filler area-is this abnormal indicative of some impending problem or is just normal because the fuel injection system is pressurised?
the only notable symptom is an intermittent loud buzzing from the the electric fuel pump.

anyone.
:confused:

Your fuel system is pressurized...you should hear a "woosh" sound when you unscrew the gas cap. This will be more noticeable on hot days, when the expansion pressure is greater.

As far as your noisy fuel pump...not related. But how noisy is the pump is a subjective question. You SHOULD hear the pump operating, but it's more of a hiss than a buzz.

A buzzing pump generally means it's wearing out, although many members here have buzzing fuel pumps that operate normally.