First of all. What kind of microphone
are you using when you talk to Hal?
If it is a simple desktop mic, then that may be your problem.
Desktop mic's pick up sound from all directions, so it would
most likely be picking up not only what you say, but also
what Hal is saying in response.
The best setup for using voice recognition with Hal, is to
use headset speakers that also have a noise-cancelling microphone.