The hum noise is kinda loud to some of us and may not loud to other.
I been working on the hum for couple days now, Well let me say the pump it self is quiet almost silent. The problem was the pump is hard plumb to the base of the skimmer and make loud hum.
What I did was I modified the connection between the pump and the base of the skimmer with a silicone tube and it worked (SILENT)
Also, I found that depend on how you connect the pump to the skimmer. Sometime you have to twist and sit it a bit to get it quiet down. But if any pump hard plumb to any box it will HUM a bit.
So far I still think it is one of the best skimmer for the price.