First post! I've done a lot of reading on other threads but couldn't find another problem similar to mine. For a long time there has been a faint 'marbles in a paint can' type noise coming from between the engine and transmission. It's been on a lift and listened to with a stethoscope and the noise was pinpointed to be from there on 2 different occasions. The starter went out around 150k miles and I replaced it. It chipped a tooth or 2 on the flywheel when it failed but it was very minor. The noise was there before then and after the starter going out. I'm getting the rear main seal done now and asked the shop to diagnose it since they were pulling the tranny. In the end they said the transmission is in great shape (aside from it starting to leak from some of the seals) but they don't know what's causing the noise. But if I wanted to throw money at it I could start with the flex plate and torque converter (lol). In the video you can hear it most clearly in the last ten seconds or so. If anyone has any thoughts I'd really appreciate it.

 

I cant tell if thats the exact same sound I had but I had issues with the flex plate on my GS300. Im not sure if the 400 is set up the same but there is an inspection hole to see the flexplate. I had the car up on a hoist and when the engine was running I could hear it coming from the flexplate area. When I turned the car off and taped the flexplate I could hear the noise. I also had to do my rear main seal so when my mechanic dropped my transmission the flexplate was cracked all around. Not sure how that thing stayed together

 

Good thing you caught that before ripped itself in two cause that would have been a pretty crummy day. They pulled the flex plate and I went to inspect it. No cracks and looks to be in really good shape. But I should probably just replace it since its out, right? Seeing as how its only a couple hundred for a new one and its already out.

 

i had an aftermarket torque converter not too long ago that made the same noise. most prominent when i was leaving the garage in the morning and the walls help amplify the sound. or next to a wall in a drive thru. once i put the stock converter back in it never made the noise anymore. and my flex plate was not cracked. i know bc i did it myself.

 

im getting the torque converter replaced and should have my car back tomorrow. sounds like this should be the right fix, thanks guys! I'll update the thread tomorrow with the results

 

Honestly it sounds like a heat shield to me. There are shields all over that car that can come loose.

 

Check for loose internal cat rattle and ^^^ heat shields good luck let us know

 

Welp, it wasn't the torque converter I've checked the heat shields before but I will definitely get them checked again. As for the cat.... thats actually pretty possible too as i do get the random p0420 when i drive too much in the city and too little on the freeway. Also I passed smog by 1ppm in the HC's last time. I had 48 and max is 49. The time before that it was 40 and the time before that it was 23. How would I check the cat? Give it some gentle taps it and listen?

 

Does it change when the engine is cold or hot? If so, it could be a cracked catalytic converter. They are located right by the transmission as well.

 

It's pretty consistent whether it is warm or cold. It's heard around 1800 rpm +/- 200 or so and in park, neutral or in gear. Could it still be a damaged catalytic converter?