It sounds to me that you may have lowered the action, either from the saddle or the nut,maybe changed strings to a lighter guage to the point the strings are "sizzling" along some or many of the frets which would give what I would discribe as a harpschord effect. That symptom would increase if you had also made an adjustment to the truss rod in addition to any of the other procedures mentioned above.Can you tell if the guitar has any "backbow" in the neck? The guitar should probably have a slight bow (concave)or "relief" in the neck and changing the gauge of the string alone could cause that.