Snooki storming out of the "Jersey Shore" house and threatening to quit was caused by some bad blood with her old foe, Angelina Pivarnick.

Sources close to production tell TMZ ... Snooki and Angelina got into it HEAVY while shooting 'Family Vacation' Tuesday night. The fight escalated slowly inside the house before the ugly scene in the video TMZ first posted of Snooks marching out, screaming.

We're told Snooki decided to remain at the house after her blowup. She returned to shooting Wednesday with the rest of the cast, sans Mike "The Situation," of course. It at least appears the women have made up. We got footage of the gang walking along the pier, and Angelina and Snooki cordially walked side by side and chatted.

Our sources say their altercation stemmed from some past beef with Angelina bubbling up, and though producers tried to calm the situation for a while ... Snooki ultimately bolted.

We broke the story, she was heard yelling, "Leave me the f**k alone, this is why I didn't want to do this s**t. Leave me alone!" before adding ... "I hate this s**t" and saying she wanted to go home to her kids.

We're told it's been harder and harder to get the cast together with their growing families and personal drama in their lives, and Snooki's meltdown was just more proof of the challenge.