I just finished dropping in my new motor and I also installed a new engine wiring harness. Today was the first time I put the battery in to see if there was power to the system. When I turn the key to the "On" position, this awful whining/whistling noise starts up. Its coming from the passenger side of the dash, seemingly right where the ECM is mounted. It sounds a lot like the noise my heater made when the vacuum lines were cut and it had no signal. What in the world does this mean? Thanks.

It's not some kind of buzzer that's dying is it? I don't know of anything else under there that would make a noise like that. It might have been the heater fan. Other than that....