  In a variant of the Randall-Sundrum braneworld model which has a charged
black hole in an anti-de Sitter bulk, the 4D speed of gravity depends upon
one's location in the bulk, and in general differs from the speed of light on a
given 3-brane. We apply phenomenological constraints on the difference in the
speeds of light and gravity to models which use the warping to solve the
hierarchy problem. In particular, consideration of the gravi-Cerenkov radiation
of Kaluza-Klein gravitons by ultra-high energy cosmic rays leads to a stringent
limit on the fractional difference between the graviton and photon speeds in
RS-like models: it must be less than a part in 10^{23}.
