Have my fuel pumps died on my 190 ???

[16valvedave]

Hi.
I have a 190E 2.5-16. A couple of weeks ago my car just died and left me stranded by the side of the road. At first i thought it was my fuel pump relay because i could not hear my fuel pumps energize, and they normally make a good loud buzz.
When i finally got the car home i jumped the fuel pump relay socket and got underneath the car and to my suprise both my pumps were indeed running, so why have they gone all quiet ? You can only hear them when you get your head right next to them.
I put my relay back in and got a friend to turn my ignition on whilst i stayed under the car, the pumps did run for a second or so as you would expect them to. So that ruled out a faulty relay. I then took the pumps off the car and connected them directly to 12 volts and they both run but only whisper quiet.
Is it possible for both pumps to die at the same time ? if indeed they have died.
They are certainly not giving me any fuel pressure or making their usual sound.
The pumps were replaced only a couple of years ago with genuine bosch parts and have only covered around 8 thousand miles in that time, so i wouldn't have thought they were ready to die just yet.
Can anyone shed any light or give me any ideas as to what i might be missing with this problem. I dont really want to shell out for 2 fuel pumps just in the hope it may fix it. I would rather be sure.
Thanks in advance for any help i may receive.
Dave