2005 Santa Fe - alarm stuck in a loop, 'dead' battery and now the radio won't turn on
 

I have a 2005 Hyundai Santa Fe. Came out this morning and heard a 'chirping' noise - the same noise the vehicle makes when you arm the security system using the fob. Except I hadn't used the fob, and the chirping sound kept repeating, as if it was stuck in a loop. I then tried using the fob to unlock the vehicle, but it didn't work, so I used the key to open the door.

The chirping continued.

I got in the vehicle and tried to start it, and nothing happened. I called a friend to come and give me a boost, as I figured the battery was dead, due to the 'chirping' from what I assumed was the security system being stuck in an 'arming' loop of sorts.

When they started the boost, the alarm finally activated (that's fun at 730a), which I then turned off, using the fob. I put the key in the ignition and the vehicle started fine, and the 'chirping' stopped. However, now the radio will not turn on.

I did not use the fob to lock the doors when I arrived at work, and the 'chirping' has not started again.

What the heck happened? I can see no signs of someone trying to break into the vehicle, and I don't remember it making the 'chirping' noise last night when I locked the vehicle.