How old is the house? Wonder if it could be an old well room. In my area it was common to have well rooms with pump equipment, even for houses built in the 50s. When houses went to city water, mostly they just removed everything and cemented over the well pipe. But it seems plausible that someone just sealed the whole room up if that for some reason seemed easier. The house I grew up in had some kind of well room machinery that had to be removed in the early nineties and I recall it being a big to-do (though I was a kid) based on the size/weight and room dimensions.