So I'm at a stoplight, don't launch hard. I get to about 15 mph and gun it. Shift into 2nd, loud KNOCK sound, like something hard striking against glass, and I'm thinking it was my keys on the dash, so this may not even be part of the issue. Note I only heard the sound ONCE. So it's not engine knocking constantly. I remain on it for another 5 seconds since it doesn't do anything else strange. My girlfriends asks if I heard the knock. I did. I didn't really think about it until a few seconds afterwards.
I take a right turn, go half a block, take a left turn into a parking lot, put in the clutch to shift into 1st from 2nd, and my car shuts itself off. I notice this because my power steering (and the lights) just turn off. I hold in the clutch and turn it back on (while rolling) and park.
I go into the movie (it's dark out, no flashlight or tools, and it acted fine once I started it back up). Come out 2 hours later. Everything is fine. No CEL or anything strange. Acts completely normal. Now I'm thinking the loud knock could've been my keys hitting the dash during the 1-2 shift...but maybe it's something else. The thing that really worries me is it turning off while driving, and no CEL or any other odd behavior after the fact. I'll keep an eye on it tomorrow on my way to work and keep my fingers crossed (it's my DD).
ANY idea what I should be looking/listening for? Has this happened to anyone else? I definately don't want to be driving down the highway and have it shut off on me again. Lack of power steering could've been deadly on the highway. Thanks for your help.
EDIT: No mods. Completely stock 2006 STI.