Loud transmission tapping?

Recently changed my oil and something in my 3.4 has started ticking/ tapping really badly at idle (up until around 1k). I don't think it's the engine because it only happens when I'm in drive or reverse but other than that I'm completely out of ideas. It sounds like a knock from inside the cabin and its most noticeable from the back. Trans fluid is bright red and the oil I changed out didn't have any metal in it. Along with this there are no check engine lights or codes, I can post a video of it later. Doesn't really sound like a flex plate either. Anyone have a similar experience? Engine is at 140k

 

you mean you hear a tapping sound when giving it gas from a green light? or just idling? 1000rpm is a high idle

 

No, the idle is around 600, it's audible up until around 1k. And not really during acceleration. It's most noticeable when I'm in drive sitting at a red light or something.

 

So from a dead stop once you get going you hear a tapping sound? Could be exhaust header or ujoints in drive shaft. When was the last time you greased the whole underside? Check exhaust header for cracks.

 

I greased up the driveshaft the oil change before last, and i checked the headers and they sound fine. It's only really audible if I'm completely stopped and in drive or reverse, in neutral and park it's dead silent. From outside the cab it sounds like ticking, and from inside the cab it's got the same tick accompanied by a deep tap.

 

Automatic? Cracked flex plate is a potential cause. Video to compare

https://youtu.be/nwPhEMmDFEg


Mind you this one’s pretty loud. I’ve heard them quieter when the cracks small