Hearing two fetal heartbeats...twins?

I have a heartbeatt doppler at home. I'm 16 weeks and noticed last night that i hear two different heartbeats. I've always heard mine and the baby's. The baby's which always sounds like a fast washing machine was registering at 162bpm...then about 3 inches over I heard another heartbeat that sounded like galloping horses and it registered at 152bpm. Tried it twice and heard them both again?!?! My maternal grandfather was a twin...am i going crazy or is there a possibility?