Washed the car this morning. Afterwards, I noticed a random nut in the driveway. Then I recalled a small ping sound as I rolled my car out of the garage before washing it. I saved the nut in my shift boot, and drove the family to church. When I parked, there was a loud metal thud sound. After church, I jacked my car up and investigated. It turns out the top nut to the passenger-side end link had decided to back off, and leave the end link hanging in the wind... Some of the threads on then end link were damaged. I gather this was from this possibly being a problem longer than I knew about (loose nut, and threads rubbing in the hole of the strut tab). Luckily I was able to get it threaded back on, and fixed.