Different Engine Noise

So yesterday I popped the hood to see if the A/C short cycles when the engine is cold like it does when hot and suddenly there was a sound I've never heard in an engine. Not the tick of the injectors, not the valves, but a loud hollow sound like a woodpecker. It made that sound for about 10 seconds then stopped, then again for about five seconds. Any clue? Again, totally different hollow woodpecker sound I've never heard before.

 

"Hollow woodpecker" love it

I think you're just hearing the engine switching between DI and port injection as part of its cleaning cycle.

 

I didn't know it had a cleaning cycle. Definitely an unnerving sound.