RO Plant causing disturbance

We live in an apartment top floor. The builder has installed a RO purification system directly on top of our floor 5 years ago. We were not informed about that while purchasing the flat. The RO plant was installed without proper sound proofing and since then we have been suffering with the sound caused when the RO plant starts functioning. We have been continuously asking the apartment association to take necessary steps to reduce the sound from the past 5 years. My parents are getting old and from the past few months they are facing lot of problem with the RO plant disturbance. When I informed the same with the association, they said that the builder installed it, you should have opposed it then, now we can't do much about it. They are asking me to submit a request letter to the association to move the plant to a different place or permanently remove it and only if the majority of the apartment people agrees they will remove the plant or bear expenses to reduce the sound, if we do not get the majority we have to bear the sound. If the options given to us do not work, how can we proceed legally in this matter?