i hear a clicking noise when driving under 40mph? could that be brakes? on 1998 Mercedes-Benz ML320

or low on transmission fluid?

Asked by for the 1998 Mercedes-Benz ML320
does it go away if you touch the brake pedal lightly?
yes, the only time the truck makes the noise is when i press the gas peddle.. If i come of the gas peddle the noise goes away.