We also have one airframe which is freaking noisy when compared with the other aircraft.
Switch OFF the Left Recirculation Fan and see what happens. It greatly reduces the level of noise.
Switch OFF both Recirculation Fans and .... marvelous, all the noise goes away.
We do it mainly on the ground as, once in the air, the noise becomes a bit more bearable.
Hope this helps
PS. The FCOM goes on to say:
"A slight increase in fuel consumption occurs for each fan that is OFF"