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.
Brass instruments do not get their name from being constructed of brass, but rather how the sound is produced. In these instruments, sound is forced through brass fixtures to create a unique sound. Tubas, trumpets, horns, and trombones are examples of brass instruments. It is important to note that saxophones are not, despite the fact that they are often made from brass, as they produce sound from a reed.