knock on startup

Daishi

It is about 20-22 degrees outside this morning started the car up while i was at home everything ran fine the clutch was a little slow to react since it was so cold out hard to explain but i babied the car on the way to work. After I got to work and shut the car off.. waited a few seconds then started it back up again dont ask me why i just felt like doing it but this time when starting it made a knocking noise its hard to explain. I started and turned the car off a couple more times and it did it like twice more it happens as soon as the car turns over. Waited a few minutes and started the car again and no noise.. not sure what it was. Any suggestions? I know cars can act funky in such cold weather maybe it was the transmission making some kind of noise im not sure.. BTW i checked the oil and its full.. this is the first time its ever happend and this is the coldest day its ever been so far this winter.