Just installed Weil-McLean Ultra and the 1100 standard pump that comes with it. Quiet (except for noise of water moving through the pipes) for a month then this "tone" or "ringing" noise began to sound from the piping every time the pump went on. Almost like a tuning fork noise. Very strange. The noise is carried through the pipes throughout the house, and it is definitely hard to sleep at night with it! The contractor doesn't seem to know what's causing it, exactly. On my own I've traced the origin of the noise to the junction to the expansion tank.
I'm guessing that the water moving by that particular junction is causing the pipe to vibrate at a frequency that produces the "ringing" noise, a bit like blowing across the mouth of a beer bottle: at the right air pressure you get a similar ringing noise. Would the solution be to change the pump so as to move the water at a different speed?