Cardboard tube (Kitchen roll), a length of foil and dried rice (Or peas or popcorn kernels or grit etc.)

Cut a length of tin foil (Kitchen foil) 3 times the length of your cardboard tube. Cut two cardboard discs the same diameter as your tube to use as end caps. Roll the foil up along its long side, then twist and squeeze it into a long firm straight section. Form the foil into a coil or spring shape, you can wrap it round and round a broom handle to help. Push the foil into the cardboard tube so that it goes from one end to the other. Glue on one of the end caps. Put a small cup of rice into the tube. Glue on the other end cap. Decorate the outside with paint or cover with wall-paper. When you turn the stick upside down you will hear a wonderful raining sound.

Originally made from hollow Cactus wood (Not kitchen roll), rain sticks are a south American device used remind the gods that some rain would be welcome to water the plants in Grandpa's garden. Now-a-days they are more commonly used as musical instruments!
Try making a really long one from 2 rolls taped together. Add a few small stones / dried peas / sand to the rice to make a more interesting rain sound.