Something is rattling from the transmission area. It's really loud in Park and Neutral, almost non-existent in Reverse and Drive, but still barely there. Got really loud after a highway trip for the most part.

There is a 2500 tq converter, it's a TH400, lmk if any more info is needed, any suggestions on what could be causing it?

 

Converter bolts tight? Broken flywheel?

 

Yeah, sounds like either the converter bolts or the flywheel bolts.

 

Also, did you use a lock washers on the converter to flywheel bolts? If so, this may be a problem as well.