Do Dampening & Pressure Help?
We tried to glue dampening material to the inside, where it also applied pressure to the pump’s housing. This helps, but only a little. It doesn’t really impact the whistling noise, but cuts down the buzz a bit.
We also found that the part of the noise we call buzz had subsided a bit after 70 to 80 hours of continuous operation. This speaks for it being due to a manufacturing defect. The whistling noise did decrease a little as well, but only marginally.