I don't hear mine at all when running except the water running through the lines. Maybe the polar package insulation deadens the sound but who knows. However, I can verify it is working by opening the valve on the toilet. No, I didn't get wet or make a big mess but that is with my camper. I wouldn't recommend it with others as I do not know what your plumbing looks like and you may get wet.
I can't use my sensor during the flush as it says full since the spray is hitting everything.
I too, have a clear elbow and close my black tank valve to fill'er back up a bit during the flush. The sticker right by the water connection says to NEVER do that but I guess I am a risk taker. :)