I sing along all the time if I know the lyrics, especially along with my favorite bands/songs, particularly "In the End" by Linkin' Park. I don't know why, but even if I'm not listening to that song, I still sing the lyrics randomly, especially when something happens and someone says "it doesn't really matter," or something along those line. lol
But most of the time, I sing it while I'm in the car alone, or when I'm in the shower I usually blast my favorite songs and sing them from there haha.