What is that noise?

Saturday night, before I could fall asleep, I heard this really funny noise outside the bedroom. I wasn't sure what it was but after listening carefully to see if I could hear it again, I just blew it off thinking that it was probably the water heater or something. At about 3:00am, Caleb woke up hungry. As I was feeding him, I heard the noise again! But this time I heard it several times in a row. I was very nervous so I shook Seth and told him to wake up and listen. He heard it too and he said that it was the same noise he heard before we went to bed, but he thought it was me doing something in the bathroom so he didn't think about it. We were both very worried because whatever or whomever was making this noise kept on and on! We stayed in our room trying to figure out what it was. I thought it was either an animal or our heat system was broken and making a weird noise. The noise sounded like someone beating on something, but it was the same noise over and over, sometimes it would be louder than the previous time. We realized that the baby monitor was on, so I unplugged it so that the intruder could not hear Seth and I planning out how we were going to get him! After trying to figure it out and having no luck, Seth decided it was time to go get em'. I was so nervous and scared!!! What was out there??? I stayed in the bedroom with Caleb. I heard Seth opening closet doors and checking the outside doors. I had my cell phone in hand ready to call 911. Then, Seth comes back in the bedroom with a helium balloon that had been given to us when Caleb was born. It had somehow made it's way downstairs to the living room and was getting hit by our ceiling fan everytime it drifted up to the ceiling. It had been doing that since we had gone to bed! Hahahahahaha. Needless to say we were very relieved! But we also felt like complete idiots. So now our joke is that we need to keep our doors locked so as not to let any more balloons come wandering inside in the middle of the night.