Is it buzzing or hissing?

Hissing is normal.

Some here say theirs buzz too, but usually that's a sign of impending doom.

Mine hiss audibly from the outside...that includes the R129.

My VW has an aftermarket electric fuel pump and it buzzes (since new)...and you can hear it from the inside when you start up the car...once fuel pressure builds up, then the buzz changes to a low growl...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car