In two rooms, there appears to be raised stripe between the sheets of
drywall on the ceiling. I am not aware of water damage or leaks that
may have caused this (ranch house, no rooms above). This looks to be
exactly the width of the drywall tape used.

I am not planning to re-drywall ceilings, but is there a nice way of
fixing this. Should I try to smooth it out by mudding around the
stripe?

C_kubie