I have an AO Smith 2HP 2 speed motor on a Whisperflo pump. It was installed about 4 years ago. I run it on low speed for around 10 hours per day.
A few weeks ago it started making a loud, rythmic humming sound on high speed, which is hard to hear in the video, but on low speed it sounds like there are rocks in the pump:
The noise is definitely not the motor vibrating. My water flow and pressure are normal and haven't changed with the onset of the sound.
Thinking it might be debris in the impeller, I took it apart and cleaned the impeller, but there was very little debris there. There are no obvious water leaks and I haven't made any changes to the system recently.
The sound is present 100% of the time. Even after the motor has been off overnight it makes the sound right away.