While the concept of "loudness" doesn't directly apply to planets, the question might be interpreted in terms of the intensity of natural phenomena occurring on different celestial bodies. In that sense, one candidate for the "loudest" planet in the solar system could be Jupiter.
Jupiter is known for its intense radio emissions, which are generated by its powerful magnetic field interacting with its moon Io. These emissions can be detected and converted into sound waves that we can hear. When these signals are converted into audio, they create a distinctive and somewhat eerie "roaring" sound. However, it's important to note that these sounds are not audible in space since sound requires a medium, such as air, to travel.
So while the idea of a "loud" planet is not applicable in the conventional sense, Jupiter's intense radio emissions and the subsequent conversion to sound waves can make it an intriguing candidate for the title of the "loudest" planet in the solar system.