Touch upâs should be done minimum 4-6 weeks post the initial treatment. This allows time for eyebrows to heal fully before perfecting them for the second time. Free touch-ups are only valid up to 3 months from initial procedure date.
Re: The Tinny sound? Most folks that are concerned about a tinny noise with aluminum boats are referring to the noise generated by the hull moving through the water (which can be modulated/reduced through many different avenues). You mention vibration and rpms, so I'm guessing that you're not referring to that sound.
This instrument belongs to the woodwind family, although it is made of metal. It differs from other woodwind instruments as it does not have a reed. The sound is produced by blowing across the top of a hole - a bit like blowing across the open top of a glass bottle.