Best approach is to compare sound with a full tank to the sound on a quarter tank. The transfer pump and its troublesome coupling hose is pretty much out of the picture on a full tank, so cavitation noise from the main pump will be minimum or non-existant.

I'd think there's a distinction between the humming of a pump mechanically failing and the more raucous cavitating sound of a pump starved for input, but I haven't yet heard the former and never needed to replace the main pump.

As an alternative, I believe I read about measuring fuel pump current as a diagnostic for pump failure. Maybe somewhere in the archives here? Stretching way back, I even recall somewhere oscilloscope traces posted with remarks about main pump armature damage.

While it is on blocks, you can run the pump, I think, by jumpering around the relay.
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Art Benstein near Baltimore