The Emperors are a little loud...my problem is trying to keep it level...that can cause more noise...a little piece of carbon, or LR
if you are using in, caught around the impellor can also create noise. I leave the Bio-wheel out and turn the spray-bar down towards the water to create good water movement.
I have noticed the newer Emperors are noisier than the older ones of 8 years ago also..which do you have? I haven't been able to find the lever to slow down the intake when feeding on the newer ones. The 280's anyway.