Durso Style Drain Whistling

[Wayne]

Hello all my Durso style drain started to whistle. The only thing that I changed was I added T's to the bottom of the drain tubes. The one end on the drain pipe, one end in the sump and one thats open to air. This was added as an attempt to reduce bubbles in the sump... didn't work, just more noise.

This mourning it started to whistle, I checked the hole on the top and it was unplugged. I have no other ideas. Thanks!