So some of you may already have known this, but I was surprised when I read it, so I gave it a shot:
Apparently close-celled foam acts as an acoustic amplification chamber rather than a sound dampener when a rattle is encased in it!
For example, I melted a hole through 6mm foam with a hot bodkin and pushed the little 1.5 cm rattle inside for this bass-sized wiggle bug head.

The rattle sound is at least 3X louder than the same rattle loose, or pressed between my finger/thumb pads!
The completed fly should be quite loud as this guy wobbles side to side on the retrieve

Same for this articulated swimming dragon. The bulb at the end of the tail (yeah, yeah, I'll pretty it up on the second try! The bass won't care
) is 1.5mm foam wrapped around the rattle, then inserted into heat shrink tubing with a drop of superglue, and then shrunk onto the mangum tail.
Bonus that it should waggle, rattle, and float while swimming. Looking for hogs with that one!

Second try at shrink tube tail

Wait... will Central WA bass avoid a rattling snakey thing?
Apparently close-celled foam acts as an acoustic amplification chamber rather than a sound dampener when a rattle is encased in it!
For example, I melted a hole through 6mm foam with a hot bodkin and pushed the little 1.5 cm rattle inside for this bass-sized wiggle bug head.

The rattle sound is at least 3X louder than the same rattle loose, or pressed between my finger/thumb pads!
The completed fly should be quite loud as this guy wobbles side to side on the retrieve

Same for this articulated swimming dragon. The bulb at the end of the tail (yeah, yeah, I'll pretty it up on the second try! The bass won't care
Bonus that it should waggle, rattle, and float while swimming. Looking for hogs with that one!

Second try at shrink tube tail

Wait... will Central WA bass avoid a rattling snakey thing?