Which Bronica did you try? The earlier cameras like the S, S2, and S2a were famous for their loud shutter. I use an S2a. Fortunately, most of the sound comes after the exposure.
The reason for this is the falling mirror design. When the shutter fires, the mirror, which is hinged in front, slips into a metal sheath, so that light is not reflected from the mirror onto the film, and a curtain covers the focusing screen, so that no light enters through the viewfinder, and then the focal plane shutter opens. The process is reversed and ends with a substantial thunk.
The advantage of this design is that there is more room for wide lenses inside the mirror box, because the mirror isn't flipping up, so a Nikkor-Bronica 50mm or 40mm lens doesn't have to cover as much retrofocus distance as a lens of the same focal length for Hassy or Rollei.
The later cameras like the ETR, SQ, and GS series (645, 6x6, and 6x7) went back to the simpler conventional rising mirror. The EC and EC-TL, between the older design and the new design, used a split mirror system.