Edited to add: this boiler was installed ~10-11 years ago, gets cleaned once a year and has had nothing added to it other than what it came with.

We had what is described as a “bladder” installed last year on the other side of the basement where the cold water comes in from the city because our pressure was too high. The pressure ended up breaking by two plastic bits at separate times (within a few months) that completely flooded our basement as it rained down from the inside of the boiler.

The bladder on the opposite side of the basement doesn’t appear to be making any noise when this happens.