Inside Cabin High Pitched Whine

[Smallville]

I'm happy to report that everything has been resolved. Below are the 3 issues and fixes that I was dealing with.

Problem #1 - All four door locks weren't working properly. The rear driver's side would unlock when pressing the power switch but wouldn't lock, and the other three wouldn't move at all. To fix this I had to replace all four door lock actuators. Apparently these actuators are a common problem but to have all four go out is kinda crazy.

Problem #2 - Battery drain issue. Connecting an amp meter in series with the negative battery cable/clamp showed a draw of 240mA even after letting the car sit for 30 minutes. After fixing my door lock actuators the draw dropped to 150mA (I suspect an actuator was either stuck open or preventing the car from going to sleep). Another mazda forum told me that the Eonon GA5151 headunit the previous owner installed was sold with a faulty CANbus decoder. All I had to do was switch the constant power and accessory power wires from the CANbus and now I'm reading a draw of 20mA (after waiting 30 minutes for the electronics to time out).

Problem #3 - Electronic whine coming from the backseat that would die down in sound when using the power windows. Listening carefully it was coming from right in the middle of the backseats. According to my mechanic it's the fuel pump and it's normal. I only heard it because I took my backseats out when tracking my battery drain issue. Once I put the backseats in again the noise was masked.

I can FINALLY enjoy my car. Thanks to everyone who chimed in!