I just replaced both of my pumps after noticing a subtle rattle/racket sound coming from the rear of the car. After sticking the tip of my stethoscope on the plastic fuel pump cover, it was evident that at least one of the pumps was making the noise. After removing the pumps, I noticed one of them rattled like a gourd when I shook it. I presume this was the bad pump.

Regarding your low fuel tank resulting in a reduced pressure to the pumps, I'm not sure how the input pressure affects the output of the pump, but I will say that when I slid the supply hose off the back of my pump I was surprised at the pressure and amount of flow that came out before I could bend the hose and stop it (my hose crimp tool was not big enough to reach across the whole hose). It was like trying to stop the flow from a garden hose. Unfortunately, I did have a full tank of gas at the time.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles