if the belts are making noise only when cold, or very humid outside...its probably just the tension. If they are making noise all the time, its one of the idlers/pulleys somewhere.
the belts will 'settle' in when new...you'll often have to adjust the tension after a few hundred miles. The PS/AC belt is very simple and easy to reach, the water pump/alternator is in a trickier location, but still very easy if you just installed new belts. I would suggest tightening them a few turns more on the respective adjuster screws (the big long bolts you have to loosen to remove the belts) and see if that helps. No need for concern if the noise quickly goes away after they heat up a little; thats commonly a tension issue...but like i said, if they are binding up somewhere and that is whats causing the slipping...it could be one of the accessories itself.