I recently changed my fuel filter to attempt to cure a mild stutter during acceleration. The stutter is somewhat better, but there is now a constant electric sort of humming while the car is running, which is not affected by RPM or speed. It is a bit like the noise just after turning the ignition but before the engine turns over, except not as loud. Is this the fuel pump running abnormally? I did not disconnect any part of the fuel pump and used a Volvo fuel filter. Can anyone tell me if this noise is indicating a problem?

By the way, my congrats to whomever wrote the FAQ guidelines for changing a fuel filter.

Its possible your intank pump is dying. When I suspected my intank, found a separate fuse that controls the intank pump. Started the car, then removed the fuse, I could hear the intank pump working. Then suspected the short section of hose in the tank(faqs covers these items). Replaced the hose, sock filter, and new fuel filter. Main pump got noisy. After couple tanks of gas, it quieted down. Car can run with a dead intank pump, not a dead mainpump.

I have an 87-740Turbo with the same problem. My mech replaced the in tank pump(entire assembly I beleive along with trans and mounts) and from then on I had this whine noise. Did you replace the main fuel filter or the in tank pump fuel sock? I have read pretty far back into the BB but still can't figure out howto fix this.

It was the main fuel filter that was replaced.
I also changed the engine oil and filter and disconnected the oil cooler hoses and blew air through them to get the old oil out as much as possible, but I can't how the latter could produce this noise.