Back story: I've started and turned off the engine a few times today, and drove a handful of city and highway miles. Everything was fine yesterday, as well. I parked for about 30 minutes, then started it up. There was a moderate volume mechanical noise, a bit of a repeating tap/ping, perhaps like part of a fan or belt hitting something loose. It went away when I pressed the gas, and came back at idle. I turned off the engine. The noise continued. I cut the battery (I have a switch for that). The noise stopped. I peeked under the vehicle and turned the battery back on. I saw no motion, but could hear a motor (or something similar) start and the noise came back and a slight amount of smoke was produced below the engine compartment. The noise and smoked stopped on their own 2-3 seconds later, leaving the vehicle silent.

Current situation: When I turn the key to the accessory position, I hear a solenoid-like "click" from under the hood, which is normal. When I turn the key to the ignition position, I hear a hum but nothing moves. The hum sounds very similar to the sound made when the batteries are too low to turn the starter.

I'm probably going to have it towed by AAA to a shop. That's likely to take 2-3 hours. Is there anything I can try/check before then?

 

My mechanic suggests that the starter solenoid might have gotten stuck in the 'ON' position, leaving the starter engaged. Noise could have been the starter and engine disagreeing about something mechanical, and smoke would have been the engine driving the starter as an unregulated generator and burning out a wire. Fingers crossed that he's right, as that sounds like a reasonably easy/quick fix.

 

You would definitely know if the solenoid stuck because the starter would be running. This may have been the issue as it stopped when you cut battery power. I would try replacing the starter and see what that does. Take a look at the condition of the starter gear and flywheel teeth to check for damage.