What is this horrible sound?
 

2008 A3

This grating/scraping sound has gotten worse the past couple times I've driven. This last time the car barely started, like the battery was dead (it's almost new).

Obviously I need to take it in, but wondering if anyone can tell what's wrong from the sound? The engine bay smelled like burning electronics...

It's probably the alternator... Either that or the idler pulley on the accessory belt tensioner is going bad. If it's really an electrical smell, I would suspect the alternator first. You might remove the belt a spin the thing with your hand. It should spin freely and almost silently. Any noises or rattles, there's your culprit. Also I wouldn't recommend driving it until you find the issues for sure. If it is the alternator, it very well could catch fire under the right conditions..

Thanks for the info. I'm pretty familiar with the smell of burning electronics (though it could be heated/burning plastic/rubber too I guess), so sounds like it could be the alternator. I also found a piece of what can only be described as fuzz/link just inside the alternator casing. Not sure if that's relevant. I'll take it to a shop close by tomorrow.