94 ford thunderbird mystery knocking

Alright, so my parents have my old car in the shop and they are trying to figure out what a mysterious knocking sound is. The Mechanics have no clue without tearing apart the motor or the transmission. So i thought i would ask you guys, here are the facts:

94 ford thunder bird.

Odometer has been broken for some time. (i think it went out when i pushed the tripometer)

mysterious knocking coming from around the flywheel area.

no bolts are loose on the flywheel.

the knocking changes revolutionary as the car accelerates.

There is no crack in the flywheel.

The sound is the same whether in drive, reverse, or park.

The Mechanic used a stethoscope and said that it sounded louder in the tork-converter than in the engine or transmission.