Restricting the flow with a ball valve is probably contributing to the hum. More strain on the pump. Working harder to put out less flow. My blueline has no restriction, but there is still a little vibration noise. Not enough that it is noticable. I just wanted to add in that my set up can be siplified (A LOT) to suit one's needs. It would still work placed in the stand. Liquid, a little word of advice. I had my stand built 36" tall as opposed to the standard 32". This gave me a lot of room to play when my sump was in the stand. If maintenance is easy, we're more likely to do it. I think they charged me an extra $20. Now that my sump is in the basement, this is no longer an issue. Albert, I'm pretty sure you've tried this, but you can also put padding under your pump. I cut peices of playground flooring from HD. This did a lot to stop vibration noises.