No. The little prop (an actual model airplane prop) was attached to a Freon pack that blew cold air into the cabin. I personally flew on three new airplanes which had the very same issue. Once I figured it was a harmonic, I turned off the Freon pack and the engine propellers synced. Turning the pack on caused the props to go out of sync again. MX control sent a lead mechanic on our next flight who verified my observations. After changing all the Freon pack props with a different diameter, the sync problem was resolved. My belief is that the little prop produced a frequency virtually identical to the engine driven props but just enough different that it caused a very noticeable harmonic when the prop sync was selected on. (Made a “Waa-Waa-Waa” sound) Like I said, an easy fix to a big problem.