The hold harmonic vibration phenomenon.
I must say when I looked after a Halon equipped room, the noise of discharge was never alerted to me as a potential area of concern.
I did however expect it to be loud, although the mandatory "pressure test" of the room seemed amateur and involve a lot of plastic sheets and a fan.
I would have thought though that any resolution would simply involve reshaped nozzles appropriate to the density of the gas of choice would be the fix, and not beyond the wit of the manufacturers to come up with some that do not match the likely environment they are to be deployed in.
Part of the point of the system is to protect the equipment from damage, not make a problem worse by ensuring most of the kit is destroyed regardless of fire or mildly smoking power supplies...