I have recently had an open gas fire fitted as well as a gas Aga. We are now very aware of traffic noise being transmitted down both chimneys. We live next to a busy road. Both chimneys have a mushroom type cowl on the top and my intial thought was that the top of the mushroom was reflecting sound down the flues, but a local engineer says this is highly unlikely and has never been a factor in his 20 years experience. Is there anything out there that can act as a sound absorber while keeping the flues open for continual use?