What can cause a puffing/puttering sound from the exhaust when accelerating at low RPMs?

After 40mph, exhaust tone back to normal

Here's a video of what iI'm talking about. Sounds like its breaking up


https://youtu.be/HpR3A_8vXIY

 

to be honest, i had to play that sound clip like 80 times to figure out what the heck you are talking about... sounds like an aftermarket exhaust with droning

 

thethe video doesn't pick it up much but the beginning of the clip is when the puttering starts. Its like a broken up sound. Seems like there's a lack in exhaust airflow. any Idea?

 

yah I hear the puttering; it's likely nothing is wrong. its not lack of air flow or exhaust flow..
perhaps its the automatic gearing and when under load during that specific rpm the exhaust is droning???
who knows..put the car back to stock to truly troubleshoot.

or perhaps the firing order of the engine ?
the only way to truly find out is to put the car back to stock to see if it makes the same puttering at the same rpm