Fuel pumps are either electrical or mechanical. The latter featured in old or outdated vehicles. Here’s why they may sound so loud.
It might be your fuel tank is running out of fuel, or you got it refilled with contaminated gas. Try checking for both signs; drive to your mechanic in neither case.
The pump produces less or no pressure to supply the fuel to the carburetor or the engine, causing it to sound louder for being air-locked. Your mechanic will have a better look.
As obvious, a damaged pump will be more vulnerable to impurities blending with the supplied fuel and may choke the pressure, causing your vehicle to stall in the middle of nowhere.
These three may be the reasons your fuel pump is sounding so loud. However, with all three reasons absent, we'd advise you to drive to your mechanic for a profound inspection.