ebury

I'm a Houdini noob myself and was having this same problem, which was driving me nuts.

In my case it turned out to be an issue with my mouse driver (a logitech cordless). My scrollwheel had left and right tilt buttons I was unaware of and each time I would scroll the wheel I figure I would unknowingly tilt it just enough to trigger the button (which in my case were mapped to left arrow and right arrow) and begin the animation playback.

I was able to set the tilt “buttons” to NONE in the driver settings program and the problem went away lickety-split. I'm not sure this is your problem, but it could be worth a try.

Good luck!