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.
The sound is more like a higher pitch tap of light metal on metal. It can even sound like something is rattling or lose in the motor. It can be much worse under higher revs and under load. It may be completely non existent at low revs with no load on the engine. The sound may also get worse as the engine runs in very hot conditions.