I'll start by saying that the reverse durso is probably the ideal solution, at least the most elegant. I like think about how and why these things happen.
Please someone correct me if I'm thinking about this the wrong way...
Air goes down the drain with the overflow water, and it has to come out somewhere. You probably have a nice straight shot and big bubbles are making it all the way down into the sump coming out in big noisy bursts of air.
I'm guessing that durso puts an impedance at the end with the T and slows the water down, backing it up a little. The air then looks for somewhere else to go, and it escapes up the stand pipe. I wonder if that T is critical to the design.
If your overflows already have standpipes (or even if they don't), there may already be somewhere for the air to quietly go out up top, in which case, you may be able to get away with something much simpler. Like just putting a speedbump in your driain on the way down. That'll cause a small backup in the flow, causing the air to stop and try to go back up the pipe instead of rushing down into the pump.
Here's what's happening in my overflow line. Pardon the bad pic, it was dark down there and the camera focused on the wrong thing. The flow is from right to left. You can see the flow coming to this point is at least half air. The water gets backed up just a little here, enough to send the air back up. Nothing but water (and some micro bubbles) makes it the rest of the way into the sump, and it's completely silent. I didn't put that there for this purpose, it's just a happy side effect of my plumbing.
This could be something as simple as an elbow, or the reducer like you mentioned. Or it could be something like the durso.
Sorry for turning this into a physics lesson, again I just like to think about how and why things work.
