Place a 1/4 air hose (rigid type)in the airhole will quite the noise down some.
Definately want to put airline tubing, help quiet the gurgle. Basically it lets the durso burp in a weird way. You may also have to dial down your return if there is still a lot of noise once doing the airline application.
Ray Allen
San Antonio, TX
1604 Culebra/Shanefield rba0284@gmail.com
40g Breeder Reef Aquarium