This creature is very similar to the English Peg Powler.
And there's heaps more to read: https://en.wikipedia.org/wiki/Neck_(water_spirit)

The Scandinavian näcken, näkki, nøkk were male water spirits who played enchanted songs on the violin, luring women and children to drown in lakes or streams. However, not all of these spirits were necessarily malevolent; many stories indicate at the very least that nøkker were entirely harmless to their audience and attracted not only women and children, but men as well with their sweet songs. Stories also exist wherein the Fossegrim agreed to live with a human who had fallen in love with him, but many of these stories ended with the nøkk returning to his home, usually a nearby waterfall or brook. (Compare the legend of Llyn y Fan Fach in Wales.) The nøkker were said to grow despondent unless they had free, regular contact with a water source.
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The Norwegian Fossegrim or Grim, Swedish strömkarl, is a related figure who, if properly approached, will teach a musician to play so adeptly "that the trees dance and waterfalls stop at his music".

The Norwegian Fossegrim and Swedish Strömkarlen are related figures sometimes seen as by-names for the same creature. The southern Scandinavian version can transform himself into a horse-like kelpie, and is called a Bäckahästen (the "brook horse"), whilst the Welsh version is called the Ceffyl Dŵr (the "water horse").

The names are held to derive from Common Germanic *nikwus or *nikwis(i), derived from PIE *neigw ("to wash"). They are related to Sanskrit nḗnēkti, Greek νίζω nízō and νίπτω níptō, and Irish nigh (all meaning to wash or be washed). The form neck appears in English and Swedish (näck or nek, meaning "nude"). The Swedish form is derived from Old Swedish neker, which corresponds to Old Icelandic nykr (gen. nykrs), and nykk in Norwegian Nynorsk. In Finnish, the word is näkki. In Old Danish, the form was nikke and in modern Danish and Norwegian Bokmål it is nøkke/nøkk. The Icelandic and Faroese nykur are horselike creatures. In Middle Low German, it was called necker and in Middle Dutch nicker (compare also Nickel or Nikkel plus Kobolt) . The Old High German form nihhus also meant "crocodile", while the Old English nicor could mean both a "water monster" like those encountered by Beowulf, and a "hippopotamus".

That's fine, it fits with the folklore posts, and I welcome it with open arms

They're everywhere, and are probably known under different names, like garden gnomes. there's a reason it's called Northern European folklore and not just Norwegian folklore

Yes!
And do be kind to those, they are helping you, and protecting the property

Yes he is

Húsvættir is a collective term for keepers of the household, like the English brownie, or the Nordic tomte (also referred to as Nisse). The tomte or nisse is a solitary vätte, living on the farmstead. He is usually benevolent and helpful, which can not be said about an innately mischievous illvätte. However, a nisse can cause a lot of damage if he is displeased or angry, including killing of livestock or causing serious accidents.
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Scandinavian folklore features a class of beings similar to the Old Norse landvættir. They are known by many names, although the most common are vättar in southern Sweden (singular: vätte), vittra in northern Sweden, and huldrefolk in Norway (although the singular vittra and huldra, respectively, refer to a solitary and quite different being).
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During the 19th century, Peter Christen Asbjørnsen and Jørgen Moe compiled Norwegian folk tales. These stories often reflected the animistic folk belief that preserved earlier elements derived from the Viking Age.