What could cause a fluttering/spamming under lower right rib cage?

Muscle fasciculation's. There are a few possible causes . The most common cause is simply fasciculation's or twitching of the muscles. You may or may not be able to visually see this happen. If you can see it that is the best way to confirm the cause. You can also get a similar sensation from the movement of intestines and stomach. Rarely this can also be skipped or rapid heart beats. Checking your pulse will confim.