Aluminum siding bulging out. Unsure how to fix

mine has a section like that, no leak though and only when traveling.

The siding comes in sheets that interlock, starting at the bottom working up they interlock once the first one is stapled, it holds the one above it by the tongue/groove interlock. they probably missed some staples in that section or they've rusted out/pulled out. if rusted out its because of a leak, not good. to take it apart you remove the strip at the top and work your way down. Might be worth a partial tear down to inspect.