Sometimes only God can stop the grumblings. If you have a bunch of people you deal with, a bunch of people God has called you to serve, there will probably be a time when grumblings take over. When that happens very likely you as a person won't be able to please them whatsoever. Don't try. Give them to God and let Him deal with them. Once we try to please this person, and that person, and this other person (and so forth) we have gotten caught up in a bunch of people-pleasing stuff that will get us nowhere. Satan loves to see us caught up in this kind of thing because we then aren't doing God's work.
If God is using you in these people's lives, and He's convicting through you, then the only thing people can do is listen or shoot the messenger. Most often, they will shoot the messenger. Most of God's prophets have been killed. We are no different.