First sump...noisy, sucking air...suggestions?

[FSP]

They're no better than a cap and hole on a Durso properly sized for the system. I think the over the back return is the easiest solution so far, or just dialing back the flow and living with it. Otherwise, if you're willing to drain the system, you can punch another hole in the backwall and run beananimal without worry of noise.

 

[Mathew0]

OK, so after testing my overflow to try to make it noisy, I found that if your water level in the overflow is lower than the elbow of the U, it allows air to chug in the overflow. You need your hole to be up a bit from the U, which you have. Then allow the water to fill just over the top of the U, but still below your air hole. This should reduce the amount of air going down. I would suggest using a gate valve on the overflow to tune this in just right.