jax11,
I posted a response to a similar question on another board, so I just cut and pasted it to this post. Hope it helps you out.
I replaced the eyelets many years ago with wire mesh.
Purchased at a hardware store or anyplace that sell screening for patios, just make sure it is at least made of aluminum (preferably some sort of steel).
It is cheap, can be cut with scissors, and is easy to locate.
After cutting to width, wrap the mesh around the rear expansion chamber as tight as possible until you have filled up the inside diameter area of the rear chamber, you can use a couple of staples to hold it in place so it won't unwrap while re-assembling the unit.
This method worked quite a bit better than the factory aluminum eyelets for sound reduction.