What I did when I had my 90 was went and got some rigid airline tubing and some strainers that it fit in and put it down into the pipe. That way it allowed the air to escape from inside the drain without bubbling out and making noise.
1. Make sure end of drain pipe is under water, also draining into a filter sock under water will quiet it some more
2. Reduce flow through the sump ( aim for 3-5x the DT volume)
3. Maggie Muffler
Anything more would require re working your plumbing ( Bean Animal/ full syphon )