Introductions Advice: Girls t.chattering and "neighing" w/o end

Our girls had to be separated a while ago because they had issues. They were housed in side in a split cage, each with their own 2x3 (in what we hoped to be their combined 3x4). They have been living quite happily that way for many months. We are finally trying to reintroduce them but are not having much luck. The girls aren't rumblestrutting, mounting, or anything like we've encountered with introductions normally. Instead it's this constant "squeaking / neighing / chirping" sound like sounds like they're talking to each other accompanied with teeth chattering.

All the teeth chattering has been getting me nervous. It's sustained, most definitely, but they don't yawn or face each other with intent to attack. Instead it's uneasy teeth chattering whenever they're near each other and some "almost" nips (where the first tries to nip the second's behind, but the second does a 180 and teeth chatters) After these nips the second pig (usually the same one starts the trouble) makes a short burring noise. There have been several light nips and twice one of the girls has raised her paw as if to hit the other girl's head. Then they leave each other alone and wander away for a while before it all starts again.

Even when they're away from each other, they keep continuing this strange chirping / squeaking / neighing sound. It's been over an hour and it hasn't calmed down, so I am hesitant to leave them together. Is this normal or signs that they just don't get along?