Your mechanic probably thinks it is overspeeding because he's used to the sound of 2 blade props. A 3 blade prop will have a pitch at blade passing frequency of 135 HZ at 2700RPM against 90 Hz for a 2 blade.
Assuming you are using 2700 RPM for take off, the tip relative Mach no. will be about .85. Noise is very non-linear with tip speed as you approach transonic. Just pulling the RPM back to 2500-2600 once you are clear of obstacles will make a big difference.
Efficiency is obtained by using the lowest RPM and highest MP for a given power setting and setting best mixture. For take off performance you will want to use the full rated power obtained by full throttle and max RPM.
If you want to be a good neighbour, reduce RPM as soon as possible consistent with safe operation and engine limitations. The reduced climb rate will be more than compensated by the reduced noise levels.