[91Autob4]

I just bought a 2012 LT with 94k I didn’t notice anything during the test drive but when I got home from buying the car is when I noticed the thump knock low tapping noise it’s hard to explain it doesn’t sound like spark knock or lifter noise or rod knock it’s only noticeable under acceleration and stops when the car is shifting then comes right back after shift also doesn’t do it at idle and when reviving up in park anybody have clue as to what this might be?

 

[91Autob4]

The transmission shifts smoothly and the motor has plenty of power no check engine light or codes also idles very smoothly

 

[VladThe]

I am not really a mechanic, so take this advice with a grain of salt. Plus, my responding may move this post up in importance and visibility on the forum.
It sounds like something that is shifting around only when there is a rearward g-force. Which suggests to me something loose that keeps getting pushed back into a moving part or which allows that shifted part to rattle. To my thinking, that reduces the odds of the problem being a serious engine or transmission issue, but still frigging annoying ( I have exhaust noise that only occurs on start in extreme cold and slushy/icy conditions).
Hopefully one of the mechanical wonks on here can narrow it down more for you.

 

[kbz1960]

Is it the motor or something else? Mine growls on exceleration which I've never heard in other cars I've owned.

 

[91Autob4]

doesn’t sound like the motor to me,I’m not sure what it is just yet it makes it hard to diagnose when it only does it under acceleration in gear but goes away when shifting it almost sounds like there is something loose in the tranny but I’m just guessing

 

[91Autob4]

If it was a cracked flex plate you would think it would do it in park reving it up.