I tried to find my original review for the 75i but couldn't... anyway, I wanted to give an update because I'm still so impressed with the Alen company and my purifier. I keep it on top speed all the time and the sound isn't too noticeable. It's pleasant, if anything, and helps me fall asleep. All I have to do to care for it is vacuum the outermost filter ever 2-3 months-- and I'm amazed at how much dust and grime it gets out of the air! The main filter looks a bit wild at this point, but just means its doing its job. Our air quality is so much better and I don't get frequent migraines as I used to. Before, if I swat at the couch, a cloud of dust would come up. Now, there's nothing! I'd very much recommend this!