OT because it wasn’t one of my Pentax lenses. It was the Sony 24-70/4 Z. Awfully nice optics. I read through an article on this lens. The sound it makes ... wouldn't surprise me if that AF solenoid coil came loose and was beating itself back and forth trying to focus. And since it happened just after shooting outside, there could be some contamination on the focus sensor. That’s easily cleaned. But I'm not about to take it apart ... not yet. https://www.lensrentals.com/blog/2015/04/tearing-down-the-sony-24-70-f4-za-oss-vario-tessar/ Interestingly, this guy shoot a K-1.