RE: F 161 and fin
Yes, if the fin sings, there's something not quite right with it.
I think most of the Drake fins are molded (someone correct me if
I'm wrong here) and the R-19 Formula fin that is supplied with the F-161 is just as susceptable to tiny errors (that could make the fin sing) as any other "production" fins.
The mold was made from a Deboichet plug I'm sure, but even with a very precise mold, there can be some warpage, over finishing, etc. that could induce the concaves or too thin trailing edge that causes the fin to vibrate enough to make the noise.
The Drake R-19 is still a "production fin" not a custom Deboichet R-19, or a C3 or a Kashy fin.
So, there certainly is more tolerance for "imperfections" in a $150 molded production fin than a custom, hand made, hand finished
fin that costs 2-3 times as much.
So, if it sings, I've given you suggestions on how to make it quiet and fast.
Hope this helps,