I have an '05 Sienna. At 7 this morning, it was making a knocking noise when I went to leave for work. It had been off since about 9:30 last night. Clicked unlock on the remote and nothing happened. Had to unlock it with the key. Internal unlock button does nothing as well. Turning the key, it acts like the battery is low, i.e. dashboard lights come on but are dim and the car won't crank. The knocking noise is louder inside the car than it is outside. Disconnecting the battery stops the noise, but it starts again as soon as I reconnect the battery. The sound seems to be coming from the back passenger sliding door, but since there is no way to unlock it, I can't even open it to look for any issues there.
Here is a (not great quality) video: https://www.facebook.com/kevin.camp.77/videos/10206960190140779/?pnref=story