<p>Harking back to the days of "singing disk drives," I am wondering if anyone's written music to be performed on a 3D printer. Most of us have noticed in passing that the servo motors for X and Y drive generate a different pitch depending on motion speed. With some care and experimentation, one could write g-code to produce not only a tone but even a 2-tone chord.  So -- has this been done? Does anyone want to do so? (Note that there's no need to simultaneously produce a print, but that would be even classier).</p>

Yes, it has been done before, see
here
and
here.
The README file of the first repository linked above contains a detailed explanation of the basic idea/calculations involved.  A short excerpt:
As you can set the parameters of G1 in such a way as to precisely control the velocity and the distance of a movement along a certain axis, you can control the operation frequency of the stepper motors as well as the actual time to complete a movement.
On another note (pun intended), you can also play music by using the code
```
M300
```
.