I got rid of my durso and used a ball valve on the drain to restrict the amount of water draining to match the amount that the pump puts out. The overflow and sump are totally silent because no air goes down the drain. I also learned this from Herbie's post on reefcentral and it is by far the best solution I know of.
Here's a photo of the water level staying constant between the overflow and the drain. The other pipe that you can see in the overflow box is just for backup incase the main one got clogged:
The only time I would ever recomend using a standpipe to silence an overflow is if I had one of these online stores that charged outrageous prices for something that's just pvc, or if I kept my sump in the basement where I didn't have to hear it. JMO.
- Chad