One important detail!!
At one point of the movie, Mike intentionally disconnected the power from the outlet(placed right next room to the machine being operated) so that he could have an excuse to go listen to the tapes again. However he was interrupted by Phil who called him away, leaving Jeff to check the breaker box in the basement. Later we did find out that the breaker box was unplugged when Jeff got down there(right before encountering Hank in the staircase). So I'm wondering if that's a hint that there was indeed something supernatural at play. Although personally I'm subbed to the psychological explanation.
Any thoughts would be appreciated :)