SWC-160 + Pinwheel - LOUD when air is opened up

[R_MC]

Hi All, I have a SWC-160 skimmer and am using a pinwheel impeller. The skimmer is currently sitting in ~6 inches of water. The more air given, the louder and "grindier" the impeller. Also, less froth is produced as more air is allowed. When closed up quite a bit the produced bubbles are not very fine and so the skimmate production is poor.

 

I have two of the replacement pinwheel impellers and both exhibit the same behavior.

 

It is not an issue of the airhose being unmuffled - has a muffler and works. The sound is coming from the impeller.

 

Any tips?