I've never been able to stand the noise my rainbow makes on low speed. It's like this weird pitch like you're getting an ear test or something. Not bad at first, but it becomes maddening after a while. It has always been this way. On high speed, it purrs. There's nothing wrong with mine at all. I think that's just the way it is. Luckily, I don't have a need for low speed. Honestly, I don't even think it can possibly do much with so little air going through the machine. Besides, if I vacuumed and dusted my house with it, there's no need for it because you already got all or most of the dust.