My W124 has 132K miles on it with the original pump. Still "hissing" and not "buzzing".
I will add that I have an aftermarket electric pump on my VW that buzzed even when new...moreso when starting the car and initiating fuel delivery, and then the buzz was a bit muffled...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car