i got a 300 hooked to a 3 speed auto. when im slowing down, there is a loud knocking sound coming from under the truck. I mean i can feel it in my feet. it sounds like a belt being smacked against my bed. the faster im going, the faster the noise, and sometimes when i shift it makes the bang sound once. i was thinking the transmission is going dead or the torque converter is dieing. it doesn't happen every time i slow down or everytime it shifts, but i think my transmission is gonna blow up sometime soon.
the transmission has plenty of fluid. it only happens when i slow down and it doesnt happen every time i slow down, but its getting to be more and more common.
if you know what this sound is or if this ever happend to you, leave a note, or if you have a good idea of whats going on.

 

I would take a look at the actual transmission mount. It could be broken and jumping when under a good amount of stress like slowing down.

 

found it out a week or two ago, i just forgot about this thread. the problem was the rear end. the spider shaft came loose and was being grinded to hell by the spider gear. i dont know if those are the real names, but its a shaft in the readend differentual thats about five inches long and about a inch and a half in diameter my dad assumed i was doing hole shots, and he said the ford 9" was ideal for doing that. well anyways we got a new 3.08 for 200 in perfect condition.

 

Glad to hear it!