could be bad bearing, slipped collar, damaged bearing carrier allowing split rings to pop out.. bad split rings, etc.
you will need to drain hyds and rear end to pull her, and make or have a new pto shaft gasket on hand to go back in. IMHO..i'd put a new seal in her too.. they are cheap..
many times a telescoping pto shaf thtat is too long can damage these.. or one that does not slip apart can snatch on them too.
post back if you need help.
drain oil(s).. then it's a 4 bolt job. probably 30m with the seal change... seal is less than 15$.. or was..