Classic/Antique Car Repair: noise in engine, torque converter, flex plate

Question
QUESTION: I have a 1951 packard 327 engine that has just been rebuilt. the engine sounds perfect at idle and under operating temperature. when engine reaches operating temp it has a raddle/noise around 1300rpm. idle no noise. the machine shop has rechecked clearances 5 times, replaced all the lifters and cannot locate problem. thanks for any help.

ANSWER: Ok, is the noise there under no load or can you hear it when driving? Does it go away over 1300 RPM? What about the sound of the engine say at 2500 RPM? Let me know please and we will go from there.
Brad

---------- FOLLOW-UP ----------

QUESTION: thanks for your reply, the noise does not go away above 1300rpm. you can hear it driving, it only goes away at idle.at 2500 rpm the noise is still there. thanks for any help.

Answer
Ok, here is how I would approach this noise. First I would use a mechanics stethoscope checking the water pump, generator, and the engine timing case. I would then disconnect the fan belt and run the engine at the speed and listen. Then with the engine running and the clutch depressed put the transmission in gear and rev the engine up and listen. If the noise goes away when doing this the problem is in the transmission. Is this an automatic transmission car? If so the problem could be loose rivets or bolts between the flywheel (flex plate) and the torque converter.
Brad