Hi, Squeeze
The Windows speech engine is picking up other sounds that it's interpreting as human speech. Some things that can cause this are environmental sounds (including breathing and lips smacking) and/or a mic that is too hot.
VoiceAttack adds a bit of help for that. You'll want to see the option, 'Recognition Prefix Exclusions' on the Recognition tab of the Options screen. I would add, 'F' to the end of that: if;but;the;but the;to;F This *may* help. You'll want to also try moving your mic away from your mouth a little bit more and/or turn the mic volume down a bit. Something else to try is retraining your speech engine. Worst case scenario is you will need to change your affected commands to include the F at the beginning. So, instead of having just 'grant landing permission', you would have, 'grant landing permission; f grant landing permission'. These are all bandaids of course - you'll still want to figure out what is causing the extra noise.
Hope that helps!