To be honest, the noise at the start drove me nuts too. The issue is the water cascading into the socks. The goal is to somehow get the water to trickle down something into the socks, whether that be by slowing the flow or adding something that wicks the water down that would normally have flowed into the middle of the sock.
There are several things you can do. I will outline 2 options that I would try:
1 - Filter Floss - This is what I do. Cut some filter floss to a bit bigger than the sock opening, and shove it into the sock so that the water going into the sock hits the floss and trickles down it. Makes it MUCH quieter, but adds more maintenance as the floss gets clogged in a couple days. I tend to change my floss every 2 days and socks every 4 days.
2 - Recently I found that GEO sumps manufactures a “sock silencer” out of acrylic. This appears to channel the water into smaller drips into the socks rather than a waterfall. I don’t have experience with them yet, but they intrigued me when I saw them.
http://www.geosreef.com/product/felt-filter-sock-with-geo-silencer/
I hope that helps!