I'd be interested in seeing your disperser. I'm pretty sure the noise is pretty much exhaust driven as the cannister noise was a lot more tolerable and the level was very acceptable. One guy at a contest thought it was a ys, the land owner of our local club said he thought it was as quiet as the electrics. I'm also thinking a prop with a little more load could help change the exhaust sound. Hard to find a carbon prop to fit the bill. I'd kinda like to stay away from the apc as I don't need the nose weight. PT makes a 21x10 I may give a try.
I've avoided the soft mount because of the added weight. Another 3oz up front coupled with the 4oz weight of the motor extensions would be tough to overcome. I've already moved all servos to the tail. I also feel that's why we see so many broken headers. I've been trying to think of a way to get rid of the motor extensions. That would help a lot.
Hmmmm... My whole mount including the stand offs weighs less than 4 ounces. I've written before what I do with mounts but may be worth repeating.
The stand offs are 5/16" hex with 8-32 threads, 1 1/4" long I think. McMasterCarr off the shelf item. The mount is the rubber iso mount I've discussed many times before. Its weight is around 2 1/2 ounces. I use 8-32s because the soft mount doesn't require any heavier for this small engine. Probably could use 1/4" hex and 6-32 bolts on 30cc class since I use the 8-32 on my 55 and 60 cc soft mounted set-ups too. The typical 10-32 is fine only for hard mounted set-ups; it's considerably heavier and the stand offs are very heavy. My 4 stand offs are about 1 1/2 ounces.
The OS GT 33 turns the apc 20.5x10 PN very well. From what I hear from my YS toting friends, as well or better that the 185 turns this prop.
The only 3 blade I tried was the 18x10 Mezjlik. This carbon prop just wasn't enough load and it was louder than the apc props so I stopped using it after break in. Been wanting to put together a 19x11 3 blade using apc blades; one of these days when I'm retired I may get to this project