Product review (2 stars): Whining Tone at Low speeds; Broan says this is normal.
The hood has a definite tonal whine, which is louder and more annoying at low speeds and then the pitch gets more absorbed at the high speeds. We called Broan customer support to troubleshoot and they said this is just how the range hoods sound. Definitely disappointed, as Amazon reviewers claimed that it is whisper quiet at low speeds and no one mentioned a whine. I guess we will be the first to point this out!