On cold mornings when I start my car, I notice the RPMs are always a little high for a few minutes. This, I know is normal. (cold start valve is it called?)

However, I *thought* I may have heard a very light piston slap the other day during one of these cold mornings. Happened only once

7010 mi's on the car. Synthetic Mobil1 5w30 oil. Always 93 octane gas

 

Happened to me too, just the other day. It was the first time I had heard it and I've paid very close attention each time I start it up. I'm not sure if it's piston slap, but it sounds very close to it. I haven't heard it since, so I'm attributing it to a fluke. 23K miles.