New (used) lower unit, a new noise, an other variables

[Wood Zeppelin]

Apparently prop sing is when the prop's rpm matches it's own natural frequency of resonance of the blades. So to avoid this, a props blades will be very slightly different from each other (but still balanced overall). I'm not sure how the edge beveling relates to this, but that what prop shops do to fix the problem.

[Moxieabs]

Been through a lot of props(rocky Maine lakes and unforgiving sea coast), some sung, usually around 2500-3000 and others were quiet. Never had a 4 blade sing.