  Using the RXTE PCA we discovered deep dips in the X-ray light curves of the
black-hole candidates GRO J1655-40 and 4U 1630-47 during outburst. Similar kind
of dips for GRO J1655-40 were found in 90s measurements of the RXTE ASM during
the same outburst. The duration of the dips in both sources is in the order of
minutes. The occurrences of the dips observed with the RXTE PCA and ASM in GRO
J1655-40 are consistent with the optically determined orbital period, and were
found between photometric orbital phases 0.72 and 0.86. This constitutes the
first evidence for orbital variations in X-rays for GRO J1655-40. The PCA data
indicate that an absorbing medium is responsible for these dips. The X-ray
spectra during the dips can be best described by a heavily absorbed component
and an unabsorbed component. In the case of GRO J1655-40 we are able constrain
the extent of the absorbing medium and the central X-ray source.
