There are a few birds with a "hoo-eet" call. Chaffinches, willow warblers and chiffchaffs. Chaffinches are obviously easy to identify from the other two. And the songs of willow warblers and chiffchaffs are remarkably different. But when silent, these birds are more challenging to tell apart.
These were the two birds that I wasn't sure of their ID:
Bird 1. In coastal conifer woodland, several birds repeatedly call each other with repeated "hoo-eet" calls. When I see them, they fly nervously from branch to branch. It seemed rather uniformly light brown, even a bit of yellowish or olive hue. I think they are willow warblers rather than chiffchaffs. I couldn't see their legs (chiffchaffs have darker legs). The fact that the "hoo-eet" call is a slower two-syllabus sound, is probably the diagnostic telltale that it is indeed a willow warbler.
Bird 2. A sparrow-size bird, further away from this woodland, near the dunes by the coast, in scrub (with some smaller pines and birch). Bird was of a featureless brown on back and pale belly, a pointy bill, and remarkably, a pale/ white supercilium and blackish eye-stripe. Might have been a willow warbler, based on habitat and the more remarkable and yellow supercillium.