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.
Aluminum is soft, and has a funky taste. I cannot think of a situation in which aluminum is superior to either cast iron or stainless steel with a copper core. Stainless definitely has a more neutral taste; if you don't believe me, throw a few tomatoes into a recipe and see how strange things taste in aluminum pans.