Clementine includes a plugin that adds a rain sound. However, it's under a CC Sampling Plus license, which isn't considered free according to the Definition of Free Cultural Works. Replace it with an equivalent rain effect (preferably a looping one) and that will fix it.

https://groups.google.com/forum/#!msg/clementine-player/Rk89HCnfmTI/_wSl5nlIJoQJ