It's quite possibly a part of your ego having a tantrum if you're practicing coming from a more conscious place on the whole, or it might be some resistance within you associated to some emotion that's trying to be released. I wouldn't give it too much thought and simply allow these fits of rage to come and go without judgement towards yourself. Just try having these fits alone and not taking them out on others.
It has been known for me to purposely go out and drive in my car and scream for a while to release some tension
It's quite a good thing you're experiencing these fits of rage as it shows something is shifting, or wanting to shift within, and not being buried deep down like most of our emotions :)
Be kind to yourself :)