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.
Hence, shifting the valve from one position to another can produce a bang-bang sound. A less informal term to describe these components is discrete valves. This term refers to how the valves operate: they shift from one discrete position to another, such as extend, retract, and neutral.