There is no single answer to the question “Why does a hearing aid whistle?”. The whistling may be related to incorrect placement of the hearing aid in the ear, earwax in the ear canal, an inappropriate ear mold or silicone dome, problems with the sound tube or filter, the technical condition of the device, or the need for reprogramming. Phonak’s support information also identifies incorrect placement and cerumen in the ear canal among the main possible causes of acoustic feedback.