Often times when dealing with a real siphon, you will have such a rapid flow rate that a water depth that does not exceed your failsafe overflow depth would not be high enough to avoid a local whirlpool/vortex occuring and drawing air down into the water. This makes a sucking sound.
Also, due to the water falling from a height it develops a high velocity. Try using traps prior to having the water dump into the fuge to slow the flow into a pour rather than a blast. Your idea should work fine. It's similar to what I did on my own tank, which is absolutely whisper silent.
Here is a picture of the traps I'm talking about. After solving the water entering the overflow problem with a solution similar to your own, I was left with the problem of the sound of the water entering the sump. The traps silenced that.
I'm not willing to make neat CAD drawings, so you will have to settle for the real thing.
Looks great Bean, and you did a very nice job with the drawings.
-Luke