Dual Drain HOB overflow: uneven draining?

[fw reefer]

I have a HOB over flow with two 1-inch drains. I am running a mag 12 return pump with about 4 feet of head pressure and 3 90 degree elbows and a ball valve. While running my system with the normal unmodified open 1-inch stand pipes at full speed it sounds like that evil suction device that dentists use to suck the saliva out of your mouth. So, due to space limitations in the overflow box I did theStockman Standpipe modification with 1-inch square holes cut in the stand pipe VS. a bunch of smaller holes drilled. My problem now is that only one of the drains is working. I.E. one pipe is handling the full load while the other one hardly has a trickle coming out of it. The problem here again is noise. Since one pipe is "sucking" so much water it wants to pull air underneath the silencing bell cover of the Stockman standpipe and it causes that awful slurping sound. I have tweaked the air valves drilled into the end caps on top of the Stockman standpipes from one extreme to the other, but have not been able to get the drains to balance the load. The two drain pipes are at the same level in the sump as well... IE one is not submerged further in the sump than the other, so the back pressure is the same on both pipes. Any ideas on how to get these drains to balance the load so that I don't have quite so much suction on one pipe and nothing on the other?
Thanks,
Any and all responses are appreciated
:help:

 

[dogstar]

I can only think maybe the holes you cut in the STANDPIPES are not level with each other and the lowest one is trying to do all the work.....????

 

[fw reefer]

I was thinking that may be the culprit, but I thought that I had them fairly even. I'll double check them when I get back home and see if that helps at all.
Thanks for the feedback. Has anyone else ever had this problem?