Am i right in assuming it’s trying the blow the filling out, but since it’s a stainless muffler there isn’t any large-enough rustholes for it to go through, so it’d seemingly just clogging the perforated tubing?

Update: With a proper flashlight the perforated tubing inside of the muffler is perfectly clear, just’s the tip that has the above weird-looking fluffy filling. No issues then!