I had to tinker with the drain hose(s) somewhat to silence my overflows.
If you have flexible drain hose(s) try to move them around - trying different positions, allowing the water to drain to the sump different ways.
Mine works best with the drain hose sort of on an incline, sloping down to the sump, as opposed to shooting straight down. The water runs down the slope of the drain hose, discharging at the suface of the sump water level, allowing air to escape up the hose and not gurgle in the overflow hole. In other words - the drain hose is not ever completely full - there's an air passage along the full length of the drain hose that is always open.
I also ran a 3-4 feet length of 3/8" vinyl airline tubing down the drain hose, from the top prefilter hole. I don't think this does too much, but it was cheap. It seems to allow the water to flow down along this length of tubing somewhat.
I discharge one of my drain hoses onto a sponge in the sump as well. Gotta clean it occassionally, but it helped too.
The other drain hose exits into a trickle plate.
I drain around 1200-1300 gph into a 14 sump on my 75 gallon tank.
Doing these things reduced the noise to a trickling sound - instead of the Niagra Falls effect I had at first.
If possible, you may want to try getting a longer drain hose, move your overflow to one end of tank, and scoot your wet/dry over to the other end under tank in the stand.
Or not - your choice