Vibrating shifter

[Noldisx]

I have a Performance with 2 8.1 GI and DP-A drives. If I want to go to neutral the lever starts shaking just before it reaches the neutral position with a high frequency. Think it is coming from the shift cone. The engines are running with a very low idle speed. Could be that the uneven circularity speed of the engine cause this phenomenon? The design of the cone with the spiral shaft would make the cone jumping just before it looses adhesion and transmits the vibration to the shifter. (my conclusion) As far as I know this engine has no torsion damper.
Any suggestions? Two drives... same symptoms in fwd and rwd.

 

[Noldisx]

Here the video...

https://www.facebook.com/video.php?v=509365420633380

 

[Scott Danforth]

Shifting of DP-a drives is a cable to the shift bell crank to the shift fork to the cone clutches

Doubtful. I would be looking for broken zip ties in the bundle under the gunwale. Most likely a harmonic frequency when the engines drop below 600 RPM being transmitted thru the hull