The song "Silence" by the band AC/DC has a total of 4 keys. This information is based on the analysis of the song's musical structure and the key signatures used throughout the track. The key changes in the song are as follows: G Major, A Major, B Major, and E Major. These key changes are a characteristic feature of AC/DC's music, which often incorporates a variety of keys to create a dynamic and engaging listening experience. The use of multiple keys in "Silence" adds complexity to the song's melody and harmony, contributing to its distinctive sound.