I agree with Atypical_Disaster that it sounds more like intrusive thoughts than voices. I've experienced both and, at least for me, they are very different things. When I have heard voices, they definitely have the feeling of "not coming from me" - where as intrusive thoughts are ideas that form that I can't stop thinking about or that repeat over and over.

If you feel something (whether it is a voice or an intrusive thought) telling you to harm yourself, someone else, or an animal, you should definitely talk to a therapist about it. If for no other reason than to just get an outside non-biased opinion on the matter (and to make sure that you are safe).