To a point the buzzing sound is normal, annoying but normal. A common culprit on these units is the pressure switch, GM had an open recall on them 12 years or so back. Updated switch kits are still available #18038508 but they aren't cheap (around 230-240)
I haven't seen the accumulators give a whole lot of problems myself, but someone else out there might. Best thing you can do is convert to vacuum booster, check parts for sale board I think it is redregalt that sells complete set-ups.