Sound distorted when I listen to headphones since installing latest update

Ever since installing the update on my iPhone 5s, the audio is distorted whenever I try to use headphones. The sound is fine until I plug my headphones in, at which point it sounds muffled as if I am listening to the music through the walls. I have not damaged my phone recently and also tried this with two different pairs of headphones. Both headphones work fine when I plug them into other items; it only gets distorted when I plug in headphones. Please help!