Oh boy.....so did they actually replace the pumps or not? What did they do? The buzzing could have been many things but if they replaced the fuel pumps that would be the obvious place to start looking. If you take a long thing screwdriver and put the handle to your ear, you can use the tip like a stethoscope to identify what's buzzing. Obviously, keep any loose hair, clothing, fingers, away from the serpentine belts because they can tear anything caught in them.
The cooling fans could have been an active DPF regen. When the emissions filters need regeneration, the engine squirts some extra fuel into the engine which burns up in the filter and cleans it out. The car runs the fan during this time to keep everything cool, even if you shut the car off. This may have been what you heard.
Stalling would make me quite upset. Ask the dealer what the lemon laws are in your state...if the engine stalls you can shift into neutral to let it roll further if it will help clear the road. This way the engine isn't giving resistance to the car rolling.
