I'd like to hear others opinions on this, but prop chatter is not unusual, or damaging to the lower unit. My Merc 150 didn't do it with the 14.5 x 17 Enertia, but it now does with the 15 x 15 Enertia. Of course, you are probably running a rubber hub in your Yammie, I have a flo-torque inset type. You see a bit about this on THT from time to time, recommendations for ridding you of it usually revolve around trying a different type of hub. 

Now you said it was doing it while it was flushing, not in the water. Have you tried  it in the water since then? Loading is much different when you have it in gear pushing water vs spinning in air, it may not even be there in the drink. 

I would get them to check the balance of the prop,ali still needs to be balanced could be a dud one .Un balanced prop will do damage over time.

 I have just done some prop testing of my own , with a f70 yammy. 

 Its on a heavy for size haines profish, and I read up even before purchase that the combo reqs careful propping. 

 It came 2nd hand to me , with a sort of standard k series 13 3/4 x 13 pitch prop.

 On sea trials when purchased it was just wrong ( old mate original owner had done 40 hrs in 6 years!) the motor had some vibration and lower and higher noise 

 pitchs that were annoying, as well as dropping off the plane far to easy and no guts on take off. 

 I researched and found out yamma do a k series prop in whats called a pontoon series with larger ears to prop which they say you need to drop a couple of pitchs down  , and comes

  standard with the shift dampering hub as well, in alloy.

 $170 ish from chivers it was worth a try. I got a 13 1/2 x 10 1/2 pitch , takeoff was great , held plane perfect even at 12 knots or less, and bingo no more funny pitch noises or vibrations.

 However it did use more juice and ran out of legs too easy as well as being a bit too revvy for my liking.

 I then picked up the 13 1/2 x 12 pitch pontoon s.d.s and finally its done. great economy , good takeoff , no vibrations , good speed at comfy revs . 

 I sold the original k prop off , and now have my perfect prop with the near new pontoon x10 1/2 as the spare for trips away, or if I feel like pulling a tube for the girls.

 Yes it took some expense and time but gee it makes the boat from good to great, very happy.

hey guys thanks for your input.spoke to the dealer very common,for a non sds prop. and will not damage gear box.

 The chatter is due to no resistance on the prop, its only chatter on the splines, nothing to worry about.