I pulled my motor due to some slapping noises from the bottom end right near the flywheel. I know sounds can travel but that's where it's pin pointed after jacking it up and laying under it. This motor has less than 500 miles on it which is why I'm pretty pissed. After draining the oil there wasn't a speck or shaving of metal anywhere, hence to why I don't believe it's a rod or main bearings. I did have two different heads in it (mechanic's screw up) so I know my motor wasn't happy but the sound comes from the acceleration of the motor. ANY ideas or suggestions are appreciated as to what this may be. After tearing down the engine I am lost SMH.

 

Year and model, auto or stick would help?

Could be most anything but have you checked the flex plate for cracks or loose bolts? Noisy scarry thing will happen if that is the problem..... Tedd

 

This may be a starter issue. The starter is supposed to disengage from the flywheel once the engine starts, but there are some parts that can fail, keeping the starter drive gear engaged. More experienced folks can elaborate on that.
I have experienced this and the ticking turned into hard knocking. At first I thought I had a valve lifter issue, then it sounded like the bloody rods were going to come through the oil pan, but it would stop after a few seconds.
We put the car on a drive on lift, cranked it with someone down below and he confirmed the noise source was the starter. Put in a rebuilt one and it works better than ever. Had my old one rebuilt by Stellar and am keeping that one as my spare.

 

1969 Cutlass S Automatic on steering column. And the flex plate is pretty new, everything was pretty tight with no cracks and the teeth are not even works down.

 

We have gotten under the car on start up and you can see the starter engage as it should and the disengage once the car is running.