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variable knocking/ tapping noise from tanny?

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i am having an issue with the ol ram that has had me and several other professional mechanics scratching our heads for some time now... the fam and i took a trip to south carolina and on the way back i noticed a knocking noise coming from under the truck. i stopped to check it out but could not find anything obviously wrong. i continued to drive home apx 70 miles. the temp gauge never went up oil preesure was normal no loss in power shifted and drove normally except loud noise of corse. changed oil no metal shavings. the noise sounds like a nut or bolt bouncing around in the bell housing of tranny. stuck a stethascope on the engine block right in front of tranny and could not hear the noise, moved back to bell housing and could hear it plain as day.the farther back i went on the tranny the quieter the noise got. pulled the tranny out and found everything to appear normal. replaced flex plate and torque converter and still nothing has changed. at idle the noise comes and goes but gets louder whenu give it gas. if any one has any suggestions or thoughts they would be very much appreciated! thanks in advance guys
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Is this a regular, rhythmic knocking (that goes with engine speed), or a random knocking? You didn't see any contact / damage between the converter and transmission pump cover, or between converter bolts and back of block or trans dust cover? No cracks in the flexplate?
 

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The converter has a snout in the front that pilots into a bore in the crankshaft, so that is likely what was driving it (when you had the engine running with the converter pushed back).

Does the knock happen in all gears (Park, Neutral, Drive, Reverse) when at a stop?
 

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Well, it can't be the trans input shaft (or anything further back) since that's not turning at a stop in Drive. Has to be engine, converter, or trans pump. Since the converter has been replaced, I doubt that's the problem. A knocking noise would be unusual for the trans pump. Maybe a bad rod bearing or piston pin in the engine?

I'm no engine expert, but could you maybe disconnect the fuel injectors or spark plugs (one at a time) to try to find a bad cylinder? If the knock is due to the firing stroke (banging the piston against a loose pin or rod bearing) then maybe deactivating that cylinder would eliminate the noise (and thus, show where the problem is). Just a thought...

Do you have MDS? If so, does it still knock in MDS mode?
 
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