If you are looking for a fairly cheap, but good muffler, take a look at Flo Pro mufflers. I've got a set on my GMC, and I'm very happy with them, at an idle, all you can hear is a little it of a wump out of the pipes, but they sound VERY good when you get into the pedal a bit. They also quiet way down when you are cruising, unless you are going 60 mph or above, then they start to a drone a little bit, but still not bad enough that you can't have a regular conversation with anyone
