Thanks for your post, Ullman, which reminds me how many people, while reasonably good at identifying birds they see, struggle with those they hear. I look no further than myself for somebody whose visual knowledge far outstrips their aural skills in this area.
That said, the great spotted woodpecker has a fairly distinctive, crisply delivered - but not loud - 'tchick, tchick' call. Once you have heard it and learnt it, your chances of seeing more of these lovely birds will greatly increase. They are, incidentally, one of the species that keep quite vocal throughout winter. Then, in early Spring, or even as soon as January if you are lucky, they begin their characteristic 'drumming' on trees, a sure sign that better weather is soon to be with us.
Here is a web link to their call:
https://www.british-birdsongs.uk/great-spotted-woodpecker/