Did a quick test in drawing and snapping for notes worked. Switch on snapping to Grid intersection in Sketch Preferences.
This is great! However, when I turn on the "snap to grid" option and select Unattached Note, it does not snap to the grid until after I place the onto the drawing. If I place the note in the middle of a grid box, the note will snap to only the middle of each grid box and not the corner of the box. I can try and freely place the note as close as possible to the corner of the grid box, but still room for error. Is there a way to make a note snap before placing it onto the drawing?