  We study Josephson junctions between superconductors connected through the
helical edge states of a two-dimensional topological insulator in the presence
of a magnetic barrier. As the equilibrium Andreev bound states of the junction
are 4Pi-periodic in the superconducting phase difference, it was speculated
that, at finite dc bias voltage, the junction exhibits a fractional Josephson
effect with half the Josephson frequency. Using the scattering matrix
formalism, we show that signatures of this effect can be seen in the
finite-frequency current noise. Furthermore, we discuss other manifestations of
the Majorana bound states forming at the edges of the superconductors.
