If it turns not to be that, I would check that your air hat is tightened down good to the throttle body, and that the rubber gasket is still good. If that gasket goes bad, or the air hat gets loose, you will here a sucking sound under light throttle (it is the sound of air flowing into your TB). Usually goes away after things warm up and heat expansion creates a better seal. The rubber gasket cost a few bucks from most parts stores. Easy fix.