I'm glad you recorded restarting it. It sounds like the timing is too advanced. If you notice when cranking, it turns, sounds like it is going to stop, and then continues turning. Has it always done that? Do me a favor. Make sure the starter is tight. I know you did a lot of work on it, so I'm not sure if you removed it for anything.
The next thought was the timing chain. However, the timing chains are at the front of the engine which is the passenger side. Listening to the video, it does sound louder on the driver's side which is where the transmission is located. That's why I am questioning if it is something like the starter, a flex plate bolt that is loose or cracked, or something between the engine and transmission.
If the RPMs increase, does the noise do the same? I'm wondering if it is something with the flywheel, torque converter, starter. Again, the good news (at least from my point of view) is the sound doesn't appear to be something internal within the engine. It actually sounds like it runs well other than the noise.
I sent this video to another tech to get his opinion. To me, it seems to be something around the flex plate. It could be cracked, the starter drive gear may not be fully retracted and hitting off the flex plate, a loose flex plate bolt, or something between the engine/trans.
If you can, try to place the recorder right down next to the bell housing on the transmission to see if it is louder.
Let me know. Also, and don't laugh, take a rubber mallet and tap on the exhaust to make sure it isn't a catalytic converter that has come loose internally. I don't think it is, but they can make a lot of noise.
Let me know.
Wednesday, June 15th, 2022 AT 9:04 PM