That looks pretty tight for space. I dont suppose you could fit a durso in there? Perhaps the stockman might fit, not sure, havent used it before, or also the hofer gurgle buster - but I think that might need more vertical space.
Do you have a valve on the drain and tried closing it slightly? Until your drain is flowing nearer its max capacity it will be sucking in a lot of air... usually just closing the drain slightly will reduce the noise. My sump was a jacuzzi until I backed the drain down considerably.