  We study electron transport through a closed Aharonov-Bohm interferometer
containing two single-level quantum dots. The quantum-dot levels are coupled to
each other indirectly via the leads. We find that this coupling yields
signatures of an effective flux-dependent level attraction in the linear
conductance. Furthermore, we predict a suppression of transport when both
levels are close to the Fermi level of the leads. The width of this anomaly is
also flux dependent. We identify different regimes in which constructive
interference of transmission through identical dots yields a signal that is 1,
2, or 4 times as large as the conductance through a single dot.
