I agree with Mallory. I only whip my icing on high speed for 1-2 minutes and at a very thick consistency. I gently stir in additional water to thin it for various tasks. The operative word is "gently," because if you stir too aggressively when the the icing is loose, you'll kick a lot of air into it.
Some air bubbles seem to be inevitable even if you mix this way. Some cookiers let their icings rest for a few hours or overnight before they use them, or even vibrate them on top of compressors so the air bubbles quickly rise to the top (then they break them once they do)! I am usually in too much of a rush to add these extra steps, so I ice right away with freshly mixed icing and will pop any really offensive air bubbles with a turkey lacer (or a toothpick) before the icing sets up.
Best of luck!
P.S. A couple of air bubbles never hurt anyone! We cookiers tend to be too perfectionistic!