i have a 1969 c4 in my fox it has started this knocking noise very very very load irratic knock. i sounds as if you were hitting the bell with a hammer. the nosie will go away if you take the car just off idle to around 1200 rpm i took the tranny off put the bell back on the motor and started it no noise. i took of the flex plate no cracks all bolts tight i took the tranny apart a thust washer was lose i replaced the noise went away. now the pesky noise is back. i agaijn took the tranny out no loose washer i took apart the tranny anyway replaced all the washers put tranny back in and this time no solution i still have a knock. please please help me i have run out of ideas.

thanks Paul.
if you would like to hear i will be at bmp with the car sat. i plan to run it anyway as there are no issues with the car other than noise. maybe it will let lose and i will find the problem.