Hey there, this may not be technically correct and people, please feel free to correct me but I have a bubble wall in my tank so only need one inlet from my air pump. It was very noisy for some time, I tried putting tape over the other inlet which works temporarily but works lose with time. Now I just have a piece of air hose (about 40cm) hanging towards the floor outside the tank from the spare inlet, it is much quieter!
Lana
Good luck with the tank!