Bassani or Hooker Aerochamber. I have Bassani's now on one car and have had the Aerochambers in the past. Neither is obnoxious and sound mellow.

The Bassani's I have right now are quite at idle and get louder as you get on it but, still not ridiculous.

Anther idea, go on You tube and find clips of different mufflers, they have plenty on there to listen to.