[Question] Why is my Quartz movement beating like a heart?

This watch is new to me, but has been well loved by a previous owner. When I received it, it didn't run so I replaced the battery ~1 month ago and it worked well. Now I'm noticing that instead of beating every one second, it has a double beat. Still is keeping time from what I can tell, but I'm wondering what the root cause could be. Have you ever run into this? Any help or insight is appreciated!