Dyson Humidify+Cool Formaldehyde Makes Whistling Noise, Service Fails to Fix It

I own a Dyson Humidify+Cool Formaldehyde air purifier, and it produces a whistling noise at low speeds. I sent the device to service three times. The first time, the fan motor was replaced under warranty, but the issue persisted.

Despite clearly explaining the problem and providing sound recordings during the second and third service visits, I was told there was no issue, and the device was returned without any action taken.

This lack of support is unacceptable for a premium product. I am disappointed that Dyson is not standing behind their product. I expect them to resolve this problem immediately, whether through proper repairs or a replacement. Ignoring customer concerns is not acceptable.