2000 GT knocking sound

[stick shift]

Deep down knocking sound, I doubt it is a rod or piston knock. I sure hope it is a cracked flex plate instead. It runs so nice , oil is clean and it has been their for at least 400 miles. checked the converter bolts , they are tight. can't see much of the flex plate threw that little inspection plate. I removed the serpentine belt and the sound is still their. checked the harmonic balancer bolt and it was tight. The speedo says 183,000 miles but i have no idea its past life before i bought it two months ago. I think it is louder around the bell housing than the oil pan. Not much noise idling or in neutral but it is still their. I do not notice it driving along. The transmission is so bright and clean i think it was rebuilt not to long ago. Maybe somebody installed the flex plate improperly like forgetting to use the spacer plate that the flywheel bolts go threw on the flex plate
I will be very relieved if it is only the flex plate. Even a very nice 2000 GT is not worth what a good rebuilt engine and labor costs these days.

 

[08GT500]

Well, you can be certain it’s not a Rod Bearing by popping off the spark plug boot of each Cyl, 1 at a time. How’s your Oil Pressure? Deep Knocking is usually a spun Rod/Main Bearing, since they recently did some Tranny work- yes- a Flexplate crack; other issue factors in well (you should be able to see this in the Ring Gear while it’s running) in Neutral. Likely won’t run true.
If the Car runs well, has relatively good output- the Valvetrain should be ok, more of a loud Clicking/tapping noise than a knock..
If the Tranny is clean, I’d agree and say they were in there, not the greatest of signs the Car was sold shortly therafter. I’d seek out a stethoscope to pinpoint noises, better yet- a Borescope Camera you can stick into the upper bellhousing and get a good look of interference points..
Is this noise symmetrical, more frequent knocks with increased RPM’s? Have you pulled the Starter, (?)- may show evidence of Steel chips if there’s a contact point.
No other issues regarding drivability, from Motor or Transmission?