I swapped my stall for a 3800 from Circle D and 34 miles after the install and never going full throttle I have this great sound.

 

Check the converter mounting bolts. I bet they are loose. Did you locktite them and tq them to 47 ft lbs.

 

Bolts are loose or the flexplate is cracked.

 

110% promise you it's the flexplate bolts. I'm sure you left the flexplate to crank fasteners alone, but they can and do loosen up when other things are changed and disturbed. Those are the most likely to loosen up and make noise. But, you messed with the flexplate to converter bolts too and those can back out too. Get it up in the air and get under it.

On another point, how do you like the 3800 circle d? I just installed a single clutch billet one in my 4l80e while waiting for my shortblock to get redone. Had the large diameter 3200 stall before and liked it for the value it was.

 

Dude I hope that you're right. I've been on a mission looking for a Lq9 longblock because everyone has told me that it's the wrist pin or connecting rod. I'll be checking that tonight when I get home. I havent been able to accelerate the car yet. Daily driving isn't bad at all. Thanks to all you guys

 

*update* I do believe that the sound is coming from the flywheel. I looked at it and couldn't see any cracks. I did notice a slight wobble.

 

Seems like I read if you squirt some wd40 close to the crank and the noise goes away
its cracked. close to where flywheel bolts on crankshaft.

 

I'm not quite that % sure...but I have bought a couple LS LQ4's that had "rod knock" for pennies, and found this...


Sounds TERRIBLE...but the engines were fine...

 

Cut the oil filter open, and see if "some" of the brgs are there....