How to silence Elos 120xl overflow

[Ivandrago]

Hello all,

I just set up my Elos 120Xl and need some advice on how to silence my overflow its making a gurgling noise. it seems like its not getting enough air to get the suction to go down the tube. Please help me out.
Thanks.

 

[hybridazn]

Slow down the flow from your return pump

 

[Ivandrago]

i did that, if i slow it to much there will not be much water exchange between the sump and the tank