I recently got my G37 straightpiped (axleback) and reving up at certain times will cause this "quacking" sound for 2 seconds then it goes away. It literally sounds like someone is blowing a duck call. Its not consistent but it happens randomly like 3-4 times a day.

I got the muffler cut out at some discount muffler shop "Minute Muffler", so I'm not sure if they just did a ****ty job or if this quacking is normal. My best guess is that the muffler is not mounted perfectly so a certain vibration pattern from a certain rpm range is causing the straight piped area to rattle.

I was just wondering if anyone has experienced this before. Unfortunately I don't have the knowledge or tools to fix something like this myself so any help is appreciated.

 

You didn't accidentally turbo it and put a duck call on your BOV did you?

 

Could be an exhaust leak. Funny, my local muffler shop is called "minute muffler" too. Where do you live?