We construct a series of
conformally invariant differential operators acting on weighted trace-free symmetric
2-tensors by a method similar to that of Graham, Jenne, Mason, and Sparling. For
compact conformal manifolds of dimension even and greater than or equal to four
with vanishing ambient obstruction tensor, one of these operators is used to describe
the second variation of the total Q-curvature. An explicit formula for conformally
Einstein manifolds is given in terms of the Lichnerowicz Laplacian of an Einstein
representative metric.