I had to laugh when I first saw the title of this thread " noisy string silencers" . ....sort of like solid split limbs...

A few thoughts popped into my head when reading your post. First off you mentioned that they did not start making noise until after you put the Winners Choice string on the bow. Since the Winners Choice strings are prestretched then they have less give than most of the other strings on the market. This could then lead to the string emitting a higher resonance sound when the arrow is released. Think of it in terms of a guitar string. The tighter you make it the higher pitched the sound becomes.

It is entirely possible that the cat whiskers amplified this resonance instead of deadening it...as they would do in most cases. I would be curious as to how old the string silencers were. As cat whiskers get older they tend to get harder which might also be contributing to the noise problem.

Obviously, it does not really matter at this point since you installed the leeches and the sound has " disappeared" .

Hope this helps some.