out of phase

Hi all, my 2 12” Kicker 10C124 are not moving together. They’re in a shared airspace sealed box. Both are working and they’re not dangerously out of phase afaik (but I’m new to car audio), you can just see one is moving a little different. They’re powered at 2 ohms by a Alpine MRP-M450 mono amp...

I just installed a new box for my friend. When I went to tune his amp for him, I noticed that his subs were moving out of sync, and one was moving a little bit faster than the other one. The subs are two Rockford P3's and the amp is a Rockford P1000-1bd. Both subs are dual-4 ohm wired down to 1...