You say it never had a list before, now it does, and you haven't changed anything? Possibly a concealed section of the bottom, outboard of a stringer, does not have a limber hole and has accumulated water from some source - rainwater or deck wash leakage, even condensation from an A/C unit where the drip hose has come off. I've seen where this condensation filled a 5 gal pail in 24 hours.