Clunking, banging noise when starting.

Here's an odd one. Yesterday I started my 2011 Prius, about 3 seconds later (Im guessing here) I pushed the A/C button, the engine started (at the same time), and I got this horrible grinding, clunking, bucking noise from under the hood. It lasted for about 5 seconds then stopped and everything was fine. Engine ran smooth, A/C was running. I turned off the A/C thinking that might be it and started it again, again everything ran smoothly. I pushed the start button the shut down the car, waited about 15 seconds, pushed it again, all normal, again with the A/C on. I put into drive and moved forward, allowed the engine to start, no problems. Smooth operation, everything normal.
I gather it'd be a good idea to take it in, but want to know how many "on-off cycles" until a problem is erased from memory. I did drive it last night (everything ran just fine) and went through 3 "cycles".
Any ideas on what this could be? Bad fuel?? I have a 2011, with about 38k miles on it. This is the second Prius I've owned and have never had a problem before, let alone something like this.