C J Campbell wrote:

Seriously, if you want to claim that mufflers reduce noise, the onus is on
you to prove that it does.

Easy. Go to your next airfield ald listen to an aircraft with and one
without a muffler. Ok, not so easy if you've never seen an aircraft with
one. Best would be if you came to Europe and would listen to one of the
new designs. You'd be very surprized.

Stefan