[Myka]

Ah ok. Have you measured the flow? Or are you guesstimating? That's still a lot of flow through the sump for a 210-gallon tank - over 10x turnover. You could cut it down to one drain, do 90% total possible volume through that one alone and it'd probably be a lot quieter. 1250 gph through 1.5" drain isn't a lot of flow which gives the opportunity for air to build up and make noise. You should be able to get around 1600 gph through a single 1" herbie drain - often a lot more depending on how much restriction is on the line (such as horizontal runs slowing it down). Also, did I suggest to cut the drains so they are only 1" below surface in the sump? That will help flush air out.