People who are satisfied with how a change is going will tend to remain silent. People who are not happy, even if they are a small minority, will grab a megaphone and start loudly broadcasting their dissatisfaction.
If you are a change champion, expect this and be prepared for it. Figure out how to amplify the positive voices, but don’t ignore the concerns of the negative voices. People who are complaining may have valid insights. Connect with them personally, listen, and turn their dissatisfaction into joint problem solving. In this way you can turn loud, infectious negativity into a force for positive change.