2006 GM, Strange Behavior
 

I have a 2006 Grand Marquis with abour 83000 miles. I bought it used about 9 months ago. It's been very reliable.

Yesterday, something strange happened. I was pulling into a parking spot and the steering got very hard. Then the gauge cluster went dark, but the car was still running. I shut it off and tried to restart it. Nothing. Just click-click-click.

I ran my errands and came back. It started right up, but when I opened the door, the gauges went dark again. Then the ABS light came on. Then it went dark. Then the light on the Traction Control button came on but I couldn't turn it back on. Then I shut it down and couldn't restart it.

I called AAA, they came and jumped it, and he said the alternator is charging. He said to replace the battery. I made it home with no issues (it's a 15 mile trip).

Here are my questions.

I've been hearing a humming / whining sound the past few weeks that get louder as the engine speeds up. Could this be the alternator going bad? If the alternator is going bad, then how did I make it home on a dead battery? What else could that be?

The car is a 2006, and the battery in there is not a Motorcraft (it's an Exide), so I know it's not original. How could this battery have gone bad? It can't be more than a few years ago given that the car is only 7 years old.

Any thoughts?