Sometimes I figure the Monolith emitted the supersonic signal because it didn't want the astronauts to photograph it, or themselves in front of it. It's a strangely vague ending for the Floyd segment.
The monolith emitted a "single very powerful radio emission aimed at Jupiter," which is why Discovery
is headed where she's headed. I always assumed the signal was so powerful it created a painfully loud interference on the spacesuit radios.