I've not had one for many years, so if they're still making them (which is surprising to me), then I may be out of touch with their development, but back in the '90s, they were very loud, and not just sonically, but they actually vibrated the air, so you could feel the buzzing, too. It was impossible for me to ride in the same room if someone wanted to watch TV; it was too distracting and annoying. Even riding upstairs in an apartment would annoy the folks below. Not good. I switched to magnetic and then fluid, with a bout of rollers in there, too, and it made things a lot better.
Again, I may have had old, cheap fan trainers (Vetta and...Nashbar, maybe?) and newer ones may be more quiet.