It's been sitting for a week and a half while I was out of town.. went home last night to collect it, and it had a flat tire. There's both a nail and a screw in it. I opened the car to look for my tire gauge, which was of course missing, then closed and locked the doors. The horn that sounded when I locked the doors didn't sound right.. it was puny. I got in and tried to start the car, but it wouldn't start. After several minutes of repeated attempts it finally did start, but continued to make a strange noise. I didn't leave anything on in the car, so I don't think it's as simple as a dead battery. I had over half a tank of gas. I just had an oil change like a month ago. None of the indicators or warning lights on the HUD were illuminated. Any ideas? Think it could be vandalism? Or just a terrible coincidence that the engine has trouble at the exact same time I get a flat tire?