I did the whole super skinny thing and to me there's really no point in going less than 8 strands on a string, just seems like a point of diminishing returns, and lot more chance of string being nicked/cut by something sharp.
Like was just said, twists is a factor. Too many twists and you're turning the string into a spring and of course if you pull and let go it will go DOING, LOL. That's why Pierre and other makers insist on customer ordering according to actual string length and not just generic AMO number.
Also, less strands in my experience also raise the pitch, could this be what you're hearing?? Pitch and volume are two different things. Maybe the pitch is just higher and now sounds unpleasant to your ear?
You're gonna have to play with brace height and silencer placement a bunch on this one bud. String material and strand count can throw a wrench in the "recommended range". My guess is with such a skinny you may have better luck at a lower brace height than you think on that bow. Perhaps 1-4-1/2" less than whatever the recommended range on the Helms is. Also, you will need to try moving the silencers from the 1/6, 1/5, to the 1/4 points on the string and see how it changes things.
You could have Chad make you a thicker BCY-X string or have Allen at Tenring make you about a 9-12 strand Rhino, and just be real exact on what length you get, I'd take the SBD, get it set to a slightly less than a middle of the road brace, and then measure the string strung.
Trying to figure out tuning 'issues' like this is half the fun of this sport IMHO. LOL.