How can you make the noncustodial stop talking negatively about the custodial parent to the child?

You can't make that happen. It is almost impossible to change that kind of behavior in an adult who places their own needs before their child's needs. That parent is self absorbed and short sighted and too angry to see the damage they do both to the child and their relationship with the child. Many immature people use their children as weapons against the other parent by trying to alienate the child from the other parent. That tactic often backfires, making the child uncomfortable. The important thing is to maintain consistency and good communication in your own home.

You need to keep your cool and not let let the child know that it upsets you. They will avoid telling you if you become upset and the most important thing at this stage is to keep the communication lines open between you and your child so that they feel secure about telling you what goes on when they're with the NC parent. Don't engage in negative talk about the non-custodial parent and encourage the child to talk about their visit.

You may be able to defuse the situation by calmly explaining that dad is angry and having trouble handling the split up. If you maintain a calm, reasonable, supportive and stable atmosphere your child will feel the difference and trust you.