What is causing the whining noise in the fuel-pump?

Mine did that on my 740... it whined for about 2 weeks... then it went out and left me on the roadway (only time in 150k miles..).. I'll bet yours craters in 100 to 600 miles from now. Not wishing you bad luck just been there before. I hope yours lasts for a million miles!!!! but thats not how I'm betting... ps my car ran perfect with the whining fuel pump right up until it would not move another foot.

I was in my local Volvo shop recently, and they have a scope-like tool that they can monitor a fuel pump with. They can tell, by liiking at the trace pattern if there is high draw, or low or high speed, or whatever ane where in the poles of the motor these patterbs appear, and they can tell you how likely it is that your pump will fail by looking at this pattern.

I sat the tech check out the fuel pump >

The pump in my 242 just died the other day, didn't make any funny noises or anything, though the current draw was apparently excessive as the connector to the relay was melted. The pump motor runs but it doesn't pump anything, I guess the impeller broke or something.

on my 740s, when the one under the car whined, it meant the one in the gas tank was dead or dying.

The in-tank pump is connected to the fuel pipe with a bellows hose that usually fails. When the tank is less than about 1/2 full the fuel gets foamy because of the split bellows. Ordinary fuel hose is a good replacement. Check the filter sock while you are in there. The in-tank pump is cheep. Fix it before you fail the expensive one.