Belching Water Lines into my Sump

Folks,

I have 6 display tanks arranged as 3 rows (2 tanks on each level) with a 2-part sump on a bottom row (so 4 rows altogether). All of the display tanks feed into that common sump on the bottom level.

I get some burping (air escaping). Sometimes it's once every 2 to 5 minutes... sometimes it can be somewhat frequent (every 30 seconds for minutes at a time).

I have the tanks arranged such that they feed the sump with a fair amount of water velocity as the head heights are 2', 4' and 6' (yeah, it's tall).

There are 6 3/4" lines going into the sump, 3 into each 4" filter sock in the sump. Each level has 2 lines going down to the sump...

Here's a photo. Short of replumbing for multiple bean animal overflows (Which I will not do because of costs, labor and space when 6 display tanks are involved), does anyone have suggestions for eliminating the gurgling... without introducing allot of spashing?

(I moved the filter socks so that you could see the lines)

Attachment 130806

Any ideas?

I suspect the issue is that the tubing forms a broad sweeping arch as it travels under the aquariums, probably trapping air in the crown of the arch... I'll snip the tie-wraps and support them in a fashion so that they run more horizontal...

Attachment 130807