833 Advice Needed

Well, it looks like you and dgc333 have discovered the achilles heel of the 833 OD aluminum case tranny. The noise you are hearing is excessive lash in the gears caused by wear in the countershaft bore in the case. The front end of the countershaft rides in a hole bored in the front of the tranny case (no bearing). This is sealed by that little freeze plug looking thing about 2" below the input shaft.
There are two ways to fix it. Find an iron case, any iron case, as long as it's an 833 4 speed and swap your gears, side cover, and tailshaft. Second option; send your aluminum case to Brewer's or Passon Performance and have them bore and sleeve the countershaft bore.
Don't worry too much about it though, you really don't need to have it fixed until it starts popping out of 3rd gear. That's the beauty of Mopars, they give you plenty of warning before something breaks, unlike some brands that shall remain unmentioned. BTW you really need at least a 3:55 rear gear to effectively use the OD tranny.