Open Question: noise in my head wakes me up?? like mirror breaking?

sometimes when I'm sleeping, I hear a loud "SMASH" (like a mirror breaking) and I wake up. it's all in my head. It's loud enough to wake me up. But to me, it sounds 99.99% real and the only way I know it's not is because there isn't a broken mirror, and this recurs from time to time. Sometimes, the noise will be something else like a large crash. Does anybody else get this? Anybody know why?