This episode page has been compiled from the episode description at the NDR website.
Nils, Samson and Finchen are playing Ludo, when they hear a loud noise coming from Rumpel, so they go over to him to see what's going on. Rumpel is listening to what he thinks is music, more specifically the 3rd noise symphony by Ludwig van Krachhoven. Nils asks Rumpel not to listen to that noise all day, so Rumpel gets an idea: he is going to compose his own symphony.
Rumpel has set up various instruments for his symphony: cans on a string, a pair of typewriters and some horns. However, he soon discovers that he can't play all the instruments at the same time.
Rumpel decides to try and put the instruments closer together and he gives it another try, but is still finding it too difficult to reach the various instruments in time. Meanwhile, Nils, Samson and Finchen conclude that judging by the sounds they hear from Rumpel, that he might need some help. They go over to him and volunteer to help play his symphony. Rumpel is reluctant at first because they are not Grouches, but ends up accepting their help, then decides that he should be the conductor.
Before they start, Nils insists that they test their instruments first. Afterwards they start to play as Rumpel does the conducting and singing. Rumpel is happy with the result.
They continue to play, but it's starting to get out of hand for Rumpel as his musicians are starting to find it funny. Rumpel is shocked, because a Grouch symphony isn't supposed to be fun. It should be loud and horrible. Nils, Samson and Finchen confirm that it's loud and horrible but still fun. After thinking about it, Rumpel accepts the fact that the symphony is also fun for some.