I have a '91 940SE (B230FT engine) with an annoying problem: The fuel pump whines loudly. To date I haven't been able to cure this. So far, I have tried the following:

Replaced main pump. Twice. Third pump is now the quietest of the three, but still isn't QUIET. Both of the replacement pumps are OEM Bosch.

Replaced in-tank pre-pump, installed new "sock".

Replaced rubber hoses between main pump and the fuel tank (two short pieces). New hoses are high-pressure hoses for fuel injection, even though the pressure is pretty low.

New Bosch fuel filter.

New Bosch fuel pressure regulator.

Fuel pressure at the fuel rail is completely normal. Not higher or lower than it should be. (Someday I'll finish cursing Volvo for the weird metric flare connectors at the fuel rail. Someday....I haven't finished yet.)

Disconnected the power to the main fuel pump, removed the input hose from the main fuel pump and checked flow from the in-tank pump. Excellent flow, put a quart of fuel in my can in twenty seconds of cranking.

Noise from the pump is roughly the same with a completely full tank of gas or a nearly empty tank.

All this and I'm STILL treated to a fairly loud WHINE from the main fuel pump. Can ANYONE suggest anything additional I can do or check to find the culprit?