Just to be clear, are we talking about a T-7 with a steel frame, or a T-3 with a plastic frame? I've experienced the harmonic chatter with a T-3, but never with a T-7.
If it is a T-7, take the honing wheel completely off, start the machine, and carefully lift the motor away from the drive wheel. It should make virtually no noise whatsoever while running. If it is noisy, seek warranty repair from your dealer. If the noise is only present when the motor engages the drive wheel, remove the stone, pull the shaft out, lube the nylon bearings with a Teflon based spray lube and re-assemble.
If the machine is running and sounding normal in every use except when using the truing tool, loosen the Allen screw that secures the diamond tip, rotate the tip one quarter turn and re-tighten. The diamond chips are in the bronze binder in a completely random pattern. Occasionally, as they are exposed odd things happen because of the pattern. Approaching the chips from a different angle usually clears up the problem.