  Recently Maldacena and Strominger found that the calculation of greybody
factors for $D=5$ black holes carrying three U(1) charges gives striking new
evidence for their description as multiply wound effective strings. Here we
show that a similar result holds for $D=4$ black holes with four $U(1)$
charges. In this case the effective string may be thought of as the triple
intersection of the 5-branes in M-theory compactified on $T^7$.
