Okay, after two days of driving back and forth to work - No stalls when starting, pump buzzing does not start until sometime on the road, idling after startup seems to fluctuate slightly over time (idled for approximately 5 minutes in the parking lot before leaving work).
So until the thing dies from it's incessant buzzing, I don't have any idea what's going on. The only thing I can think of is the tank pump has a leak in the molded hose that I didn't see, and is sucking air into the line so the buzzing noise is from the main pump impeller cavitating/spinning in the bubbles. I could be totally wrong, but if you can imagine high-pitched gurgling, that's what it sounds like to me.

That's all I got for today. Maybe I'll take another look at the tank pump assembly this weekend, or maybe I'll just attempt to have a normal weekend rather than cavorting with gas fumes...

 

OK if the hose in the in tank pump is cracked it won't suck air into the system but would cause the main pump to work harder. Also if the tank is less then 1/2 full you would have a hard time starting the car. That being said if you keep the tank above the 1/2 way mark then the main pump will work as normal. So does the pump make a lot of noise with a full tank of gas . If it doesn't then the hose or in tank pump is the problem. After market pumps are also noisier then the OEM Bosch pump. When you installed the pumps do we assume you replaced the rubber sleeve on the pump and that the 3 rubber isolators on the bracket is in good shape. By the way if you are overworking the main pump it has the potential to overheat the fuel pump relay which will cause it to fail. It sounds like the car now runs and starts normally and the only thing that is abnormal is the pump buzzes to loud. Just a reference here but when you bench tested the Bosch pump was it quieter then the aftermarket one.

 

Didn't see what model you were working on but after replacing both pumps on my 760Ti, I found the Fuel Pressure Regulator had been damaged. Replaced it with a Chinese part (needed the car quickly) and had hard start and bogging on acceleration issues. Found the car would work normally after turning the engine off and restarting, so I bit the bullet and got a good Volvo replacement part.

Just a thought, the fuel pressure should be checked at or beyond the fuel rail, not at the pump, because of the inline fuel pressure regulator. The newer cars have a Schrader valve on the end of the rail to check fuel pressure, but our older cars do not. Also, replacing the rubber as mentioned before is a good call. Air in the fuel line causes the symptoms mentioned as well.

 

air in the fuel lines should quickly get flushed out via the fuel return to the tank.

 

Full-ish tank of gas, coming home today put it at a smidge less than half a tank, but it buzzes no matter how much is in there. Funny, there's no noise in the morning, but when I arrive at work, it's buzzing, and when I leave work, about 50% of the time it's buzzing when I start up, but even if it doesn't, it's buzzing by the time I get home. There was no rubber sleeve to replace, the bracket that holds the pump is TIGHT. The rubber isolating thingummies are all intact and in place. The Bosch pump sounded normal when I did the out-of-system test.

 

The should have been a black rubber sleeve about the length of the FP on the pump. It is about 1/16 th of an inch thick and you would have needed to slide it off of the old pump and onto the new pump. This acts as a vibration and sound deadener. If you didn't have one it was either removed sometime earlier or you didn't recognize it on the old pump. It also protects against making the clamp to tight. Then there are the 3 rubber isolators that dampen the noise. So I guess if it is running OK and only makes a loud noise then drive it until it fails.

 

One more thing I've seen and you should look at is the Fuel Pump Regulator on the end of the fuel rail. If it is not working correctly or is plugged it won't let excess fuel pressure bleed off back into the tank. This will cause high pressure in the fuel rail which will cause the fuel pump to work harder thus it will be more noisy. At idle when vacuum is high the FPR is full open letting excessive fuel to return to the fuel tank. As you increase engine speed the vacuum decreases causing less fuel to return. The less fuel that returns causes higher pressure which in turn makes the FP run harder (higher current draw). A question here is : when you 1st start the car is the FP quiet at idle. Next pull and plug the vacuum hose and see if the FP gets noisy. If so then replace the fuel pump regulator.

 

I've driven it for a while, and the fuel pump is buzzing all the time. Also, sometimes I have to give it some accelerator to start. That seems to have gotten worse as the tank has gotten emptier, so we are perhaps back at the in-tank fuel pump? I still get a nice pump humming noise from the in-tank pump, so I'm skeptical...
I mentioned replacing the Fuel Pressure Regulator back in post #20 when I noticed gas smell from the vacuum line, but I'll try your trick and see if it does anything. I'll report back later.

Today I'm troubleshooting the Fuel Pump Relay. It says "10 -03- 2000" on the side, so I assume it was made in 2000? I suppose an 18-1/2 year-old relay may be pushing it's lifespan...
I found a schematic:
http://wellread.me/files/fuel-pump-r...com-inside.jpg
is this accurate?
Assuming it is, I touched a fresh 9V battery between pins 86/1 - 30 and it gave me a nice click, but touching pins 85 - 86/2 gave me nothing, so I thought the relay was a goner, but then I noticed the diode at pin 85. Reversed the contacts and it clicks just fine. I checked the relay contacts continuity with my multimeter, and all showed a strong connection when the relative coils were triggered, so I conclude the relay isn't bad.

 

Wow. Yesterday my wife went to the store and it wouldn't start after doing the shopping. That's how this all started; car wouldn't start after work, and no pump noises, so I assumed it was bad pumps. Now all indications are that the REAL problem is the ECU. I'll get that straightened out before continuing with this.

Nevermind, my inline fuse holder was corroded and since it was broken off the mounting, it was kind of flopping around in the space between the fender wall and the power steering fluid reservoir. An exposed part of the fuse socket had managed to touch a metal part which had arced and partially melted the fuse plastic, though the fuse itself was still functional. I gave it and the fuse holder some sandpaper treatment, and the car then fired up right away. I took advantage of the situation and went down to Napa to get a sealed fuse holder that I could clip in the same spot as the old fuse holder. Works like a charm, now I wonder if a crusty fuse holder was part of the problem the whole time.
Fuel pump still buzzy though...

 

I have a thread going (no responses) about a buzzy fuel pump similar but not identical issues. Did you ever figure out the buzz on the in-line?

 

Nope, never did. I got it into an accident last October, so it is now sitting in my driveway awaiting the junkyard tow truck after I pull all the parts I want off it. I found another, same model, same year, different color, and the pump doesn't buzz on that one.
Sorry I can't help further.