plumbing troubles

[Delphinus]

Without seeing your sump in person it may be hard to speculate on causes.

However, one thing that makes a huge difference, from a sound perspective, is how the water enters the sump.

I've found that submerging the outputs (any pipe where water enters the sump) makes a very large difference.

There shouldn't be a difference between a Stockman and a Durso ... only the amount of space they take up is different. Sounds like there's some fine tuning needed. The amount of air entering the standpipe will make a difference with the slurping.