Goldfinch behaviour

Hello, first time posting so please bear with me!  There was a goldfinch on my feeder this morning behaving in a way I’ve not seen before.  It was puffing up with its head on the side, beak open, then it would get back to normal, preen, eat a few seeds then do it again.  I’ll try to attach a video and some shots from the video.  We’ve been debating what’s going on - is it ill or sunbathing?  Thank you.