Well i would say the trans cooler was not changed and hose was not cleaned out.so when the new trans was put in all that crap from lines and cooler went in the trans.the sound could be spiral snap ring came off, planet gear,thrust washer dryed up or sprag.your going to have to open her up and find out?but most re-built trans fail from old lines and coolers,change them.
just my guess or 2 cents