Things I'd check.

In tank strainer, if this is clogged, the pump will cavitate.

Check fuel pressure. If the return line is crimped, the pump will be straining against it's internal over pressure relief. If this has occurred, I'd expect the motor to go rich and trip a code though.

Does this have a " drive shaft through the fuel tank " like the W202 your car is based on? If so, these use a venturi pump to get fuel from left of tank to right where strainer is.

If there is a pulsation damper anywhere on the pressure side of the pump, a failed one may cause this noise. The damper might even be at the engine or on the fuel injector rail. It will probably look like a fuel pressure regulator if it has one.

In any event, I'd be tempted to run the pump manually then poke around the engine to see if the noise is coming from the fuel pressure regulator.