I had a similar problem. My first one was turning on by itself in the middle of the night, audio only no picture. It scared the sh... out of me a couple times while sleeping. I retuned that one thinking I was defective and got another one. The second tv did the same thing the second night, so I decided to look around for another problem but not with the tv. I noticed the cable box/digital adapter in that room provided by bright house now spectrum is usually on because when I'm done watching tv i just turn the tv off not the cable box. I tried turning that off as well and the tv has not turn on again by itself. My conclusion was that there's something with the cable device, while powered on. At least in my case end up working just turning that off. If you have that or something similar conected to it, I would suggest trying to turning off the device.
Hope that helps