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.
While decorative bells can be made of such materials as horn, wood, glass, and clay, bells that are designed to ring or to play music are cast in a bronze alloy of approximately 77% copper and 23% tin. This combination produces a tough, long-lasting material that resists rusting.