Wood bees! Yeah, my sister's house had these bungle-bee lookin' things that make holes. She found out just spraying bee killer won't do from nothin'. Ya got spray dust in the holes to kill the grubs, too.
We have a regular woodpecker pair right outside our window. They show up several times a day. And either one of them gets immediate priority at the bird feeder -- no matter what kind or how many others are there.
Woodpeckies are a tad like Slo-Poke Gonzalez (Speedy's brother) in the cartoons:
"He no worry about de poosycat; he carry a gun!" BOOM goes Sylvester.