I recently experienced a failure of the upper gear case on my
MerCruiser I/O. After the shop replaced the upper gear case and put
the boat back in our slip, I took the boat out and noticed a prominant
"harmonic whining" sound coming from the lower unit when in gear. I
inquired and was told that that is the gears meshing, and the newer
the gearings, the louder the whine can be (no, my wife wasn't in the
boat). They state it is common to I/O configurations, and may be
especially loud on new boats. All I know is my old lower unit didn't
make any appreciable sound.

Is the mechanic correct?

Thanks.

Coff